Text Processing

sort
uniq
comm
cmp
diff
tr
sed
awk
perl
cut
paste
column
pr

The rich set of text processing commands is comprehensive and time saving. Knowing even their existence is enough to avoid the need of writing yet another script (which takes time and effort plus debugging) – a trap which many beginners fall into. An extensive list of text processing commands and examples can be found here

### sort

sort lines of text files

As the name implies, this command is used to sort files. How about alphabetic sort and numeric sort? Possible. How about sorting a particular column? Possible. Prioritized multiple sorting order? Possible. Randomize? Unique? Just about any sorting need is catered by this powerful command

Options

-R random sort
-r reverse the sort order
-o redirect sorted result to specified filename, very useful to sort a file inplace
-n sort numerically
-h sort human readable numbers like 4K, 3M, etc
-k sort via key
-u sort uniquely
-b ignore leading white-spaces of a line while sorting
-t use SEP instead of non-blank to blank transition

Examples

sort dir_list.txt display sorted file on standard output
sort -bn numbers.txt -o numbers.txt sort numbers.txt numerically (ignoring leading white-spaces) and overwrite the file with sorted output
sort -R crypto_keys.txt -o crypto_keys_random.txt sort randomly and write to new file
- shuf crypto_keys.txt -o crypto_keys_random.txt can also be used
du -sh * | sort -h sort file/directory sizes in current directory in human readable format

```bash $ cat ip.txt 6.2 : 897 : bar 3.1 : 32 : foo 2.3 : 012 : bar 1.2 : 123 : xyz

$ # -k3,3 means from 3rd column onwards to 3rd column $ # for ex: to sort from 2nd column till end, use -k2 $ sort -t: -k3,3 ip.txt 2.3 : 012 : bar 6.2 : 897 : bar 3.1 : 32 : foo 1.2 : 123 : xyz

$ # -n option for numeric sort, check out what happens when -n is not used $ sort -t: -k2,2n ip.txt 2.3 : 012 : bar 3.1 : 32 : foo 1.2 : 123 : xyz 6.2 : 897 : bar

$ # more than one rule can be specified to resolve same values $ sort -t: -k3,3 -k1,1rn ip.txt 6.2 : 897 : bar 2.3 : 012 : bar 3.1 : 32 : foo 1.2 : 123 : xyz


**Further Reading**

* [sort like a master](http://www.skorks.com/2010/05/sort-files-like-a-master-with-the-linux-sort-command-bash/)
* [sort Q&A on unix stackexchange](https://unix.stackexchange.com/questions/tagged/sort?sort=votes&pageSize=15)
* [sort on multiple columns using -k option](https://unix.stackexchange.com/questions/249452/unix-multiple-column-sort-issue)

<br>
### <a name="uniq"></a>uniq

>report or omit repeated lines

This command is more specific to recognizing duplicates. Usually requires a sorted input as the comparison is made on adjacent lines only

**Options**

* `-d` print only duplicate lines
* `-c` prefix count to occurrences
* `-u` print only unique lines

**Examples**

* `sort test_list.txt | uniq` outputs lines of test_list.txt in sorted order with duplicate lines removed
	* `uniq <(sort test_list.txt)` same command using process substitution
	* `sort -u test_list.txt` equivalent command
* `uniq -d sorted_list.txt` print only duplicate lines
* `uniq -cd sorted_list.txt` print only duplicate lines and prefix the line with number of times it is repeated
* `uniq -u sorted_list.txt` print only unique lines, repeated lines are ignored
* [uniq Q&A on unix stackexchange](http://unix.stackexchange.com/questions/tagged/uniq?sort=votes&pageSize=15)

<br>
### <a name="comm"></a>comm

>compare two sorted files line by line

Without any options, it prints output in three columns - lines unique to file1, line unique to file2 and lines common to both files

**Options**

* `-1` suppress lines unique to file1
* `-2` suppress lines unique to file2
* `-3` suppress lines common to both files

**Examples**

* `comm -23 sorted_file1.txt sorted_file2.txt` print lines unique to sorted_file1.txt
    * `comm -23 <(sort file1.txt) <(sort file2.txt)'` same command using process substitution, if sorted input files are not available
* `comm -13 sorted_file1.txt sorted_file2.txt` print lines unique to sorted_file2.txt
* `comm -12 sorted_file1.txt sorted_file2.txt` print lines common to both files
* [comm Q&A on unix stackexchange](http://unix.stackexchange.com/questions/tagged/comm?sort=votes&pageSize=15)

<br>
### <a name="cmp"></a>cmp

>compare two files byte by byte

Useful to compare binary files. If the two files are same, no output is displayed (exit status 0)  
If there is a difference, it prints the first difference - line number and byte location (exit status 1)  
Option `-s` allows to suppress the output, useful in scripts

```bash
$ cmp /bin/grep /bin/fgrep
/bin/grep /bin/fgrep differ: byte 25, line 1

More examples here

### diff

compare files line by line

Useful to compare text files. If the two files are same, no output is displayed (exit status 0)
If there is a difference, it prints all the differences, which might not be desirable if files are too long

Options

-s convey message when two files are same
-y two column output
-i ignore case while comparing
-w ignore white-spaces
-r recursively compare files between the two directories specified
-q report if files differ, not the details of difference

Examples

diff -s test_list_mar2.txt test_list_mar3.txt compare two files
diff -s report.log bkp/mar10/ no need to specify second filename if names are same
diff -qr report/ bkp/mar10/report/ recursively compare files between report and bkp/mar10/report directories, filenames not matching are also specified in output
- see this link for detailed analysis and corner cases
diff report/ bkp/mar10/report/ | grep -w '^diff' useful trick to get only names of mismatching files (provided no mismatches contain the whole word diff at start of line)

Further Reading

diff Q&A on unix stackexchange
gvimdiff edit two, three or four versions of a file with Vim and show differences
GUI diff and merge tools

### tr

translate or delete characters

Options

-d delete the specified characters
-c complement set of characters to be replaced

Examples

tr a-z A-Z < test_list.txt convert lowercase to uppercase
tr -d ._ < test_list.txt delete the dot and underscore characters
tr a-z n-za-m < test_list.txt > encrypted_test_list.txt Encrypt by replacing every lowercase alphabet with 13th alphabet after it
- Same command on encrypted text will decrypt it
tr Q&A on unix stackexchange

### sed

stream editor for filtering and transforming text

Options

-n suppress automatic printing of pattern space
-i edit files in place (makes backup if SUFFIX supplied)
-r use extended regular expressions
-e add the script to the commands to be executed
-f add the contents of script-file to the commands to be executed
- for examples and details, refer to links given below

commands

We'll be seeing examples only for three commonly used commands

d Delete the pattern space
p Print out the pattern space
s search and replace
check out 'Often-Used Commands' and 'Less Frequently-Used Commands' sections in info sed for complete list of commands

range

By default, sed acts on all of input contents. This can be refined to specific line number or a range defined by line numbers, search pattern or mix of the two

n,m range between nth line to mth line, including n and m
i~j act on ith line and i+j, i+2j, i+3j, etc
- 1~2 means 1st, 3rd, 5th, 7th, etc lines i.e odd numbered lines
- 5~3 means 5th, 8th, 11th, etc
n only nth line
$ only last line
/pattern/ lines matching pattern
n,/pattern/ nth line to line matching pattern
n,+x nth line and x lines after
/pattern/,m line matching pattern to mth line
/pattern/,+x line matching pattern and x lines after
/pattern1/,/pattern2/ line matching pattern1 to line matching pattern2
/pattern/I lines matching pattern, pattern is case insensitive
for more details, see section 'Selecting lines with sed' in info sed
see 'Regular Expressions' in grep command for extended regular expressions reference
also check out 'Overview of Regular Expression Syntax' section in info sed

Examples for selective deletion(d)

sed '/cat/d' story.txt delete every line containing cat
sed '/cat/!d' story.txt delete every line NOT containing cat
sed '$d' story.txt delete last line of the file
sed '2,5d' story.txt delete lines 2,3,4,5 of the file
sed '1,/test/d' dir_list.txt delete all lines from beginning of file to first occurence of line containing test (the matched line is also deleted)
sed '/test/,$d' dir_list.txt delete all lines from line containing test to end of file

Examples for selective printing(p)

sed -n '5p' story.txt print 5th line, -n option overrides default print behavior of sed
- use sed '5q;d' story.txt on large files. Read more
sed -n '/cat/p' story.txt print every line containing the text cat
- equivalent to sed '/cat/!d' story.txt
sed -n '4,8!p' story.txt print all lines except lines 4 to 8
man grep | sed -n '/^\s*exit status/I,/^$/p' extract exit status information of a command from manual
- /^\s*exit status/I checks for line starting with 'exit status' in case insensitive way, white-space may be present at start of line
- /^$/ empty line
man ls | sed -n '/^\s*-F/,/^$/p' extract information on command option from manual
- /^\s*-F/ line starting with option '-F', white-space may be present at start of line

Examples for search and replace(s)

sed -i 's/cat/dog/g' story.txt search and replace every occurence of cat with dog in story.txt
sed -i.bkp 's/cat/dog/g' story.txt in addition to inplace file editing, create backup file story.txt.bkp, so that if a mistake happens, original file can be restored
- sed -i.bkp 's/cat/dog/g' *.txt to perform operation on all files ending with .txt in current directory
sed -i '5,10s/cat/dog/gI' story.txt search and replace every occurence of cat (case insensitive due to modifier I) with dog in story.txt only in line numbers 5 to 10
sed '/cat/ s/animal/mammal/g' story.txt replace animal with mammal in all lines containing cat
- Since -i option is not used, output is displayed on standard output and story.txt is not changed
- spacing between range and command is optional, sed '/cat/s/animal/mammal/g' story.txt can also be used
sed -i -e 's/cat/dog/g' -e 's/lion/tiger/g' story.txt search and replace every occurence of cat with dog and lion with tiger
- any number of -e option can be used
- sed -i 's/cat/dog/g ; s/lion/tiger/g' story.txt alternative syntax, spacing around ; is optional
sed -r 's/(.*)/abc: \1 :xyz/' list.txt add prefix 'abc: ' and suffix ' :xyz' to every line of list.txt
sed -i -r "s/(.*)/$(basename $PWD)\/\1/" dir_list.txt add current directory name and forward-slash character at the start of every line
- Note the use of double quotes to perform command substitution
sed -i -r "s|.*|$HOME/\0|" dir_list.txt add home directory and forward-slash at the start of every line
- Since the value of '$HOME' itself contains forward-slash characters, we cannot use / as delimiter
- Any character other than backslash or newline can be used as delimiter, for example | # ^ see this link for more info
- \0 back-reference contains entire matched string

Further Reading

sed basics
sed detailed tutorial
sed-book
cheat sheet
sed examples
sed one-liners explained
common search and replace examples with sed
sed Q&A on unix stackexchange
sed Q&A on stackoverflow

### awk

pattern scanning and text processing language

awk derives its name from authors Alfred Aho, Peter Weinberger and Brian Kernighan.

syntax

awk 'BEGIN {initialize} /pattern1/ {stmts} /pattern2/ {stmts}... END {finish}'
- BEGIN {initialize} used to initialize variables (could be user defined or awk variables or both), executed once - optional block
- /pattern1/ {stmts} /pattern2/ {stmts}... action performed for every line of input, pattern is optional, more than one block {} can be used with/without pattern
- END {finish} perform action once at end of program - optional block
commands can be written in a file and passed using the -f option instead of writing it all on command line
- for examples and details, refer to links given below

**Examples**

ls -l | awk '{print $1}' print first column of results of ls -l command
- $1, $2 etc refer to 1st, 2nd field, etc
- $0 contains entire line
ls -l | awk '{print $1" "$NF}' print first and last column of results of ls -l command separated by space character
- $NF pre-defined variable holds last field
ls -l | awk 'NF > 2 {print $1" "$NF}' print file permission and filename in two columns separated by space, provided a line has more than 2 fields (to exclude the first line of ls -l which has only two fields)
awk -F":" '{print $1}' /etc/passwd prints first column of /etc/passwd file
- -F option is used to specify the field separator, by default white-space is separator
awk 'BEGIN {FS = ":"} {print $1}' /etc/passwd prints first column of /etc/passwd file
- FS is field separator variable, by default white-space is separator
awk '{print "abc: " $0 " :xyz"}' list.txt add prefix 'abc: ' and suffix ' :xyz' to every line of list.txt
awk '{print FNR ": " $0}' dir_list.txt prefix line number and ': ' to all lines of file dir_list.txt
- FNR pre-defined variable contains input record number in the current input file
ls -l | awk '/^d/ {print $0}' filter output of ls -l for directories
awk '{total += $5} END {print total}' table.txt print sum of all numbers in column 5 of file table.txt
- by default, initial value of variable is 0, so at start total=0
- for every line, number in column 5 gets added to total
- after processing all the lines, the statement in END block is executed, in this case prints value of total variable

Further Reading

awk basics
Gawk: Effective AWK Programming
awk detailed tutorial
basic tutorials for grep, awk, sed
awk one-liners explained
awk book
awk cheat-sheet for awk variables, statements, functions, etc
awk examples
awk Q&A on unix stackexchange
awk Q&A on stackoverflow

### perl

The Perl 5 language interpreter

Larry Wall wrote Perl as a general purpose scripting language, borrowing features from C, shell scripting, awk, sed, grep, cut, sort etc

Reference tables given below for frequently used constructs with perl one-liners. Resource links given at end for further reading.

Descriptions adapted from perldoc - command switches

Option	Description
-e	execute perl code
-n	iterate over input files in a loop, lines are NOT printed by default
-p	iterate over input files in a loop, lines are printed by default
-l	chomp input line, $\ gets value of $/ if no argument given
-a	autosplit input lines on space, implicitly sets -n for Perl version 5.20.0 and above
-F	specifies the pattern to split input lines, implicitly sets -a and -n for Perl version 5.20.0 and above
-i	edit files in place, if extension provided make a backup copy
-0777	slurp entire file as single string, not advisable for large input files

Descriptions adapted from perldoc - Special Variables

Variable	Description
$_	The default input and pattern-searching space
$.	Current line number
$/	input record separator, newline by default
$\	output record separator, empty string by default
@F	contains the fields of each line read, applicable with -a or -F option
%ENV	contains current environment variables
$ARGV	contains the name of the current file

Function	Description
length	Returns the length in characters of the value of EXPR. If EXPR is omitted, returns the length of $_
eof	Returns 1 if the next read on FILEHANDLE will return end of file

Simple Perl program

$ perl -e 'print "Hello!\nTesting Perl one-liner\n"'
Hello!
Testing Perl one-liner

Example input file

$ cat test.txt 
abc  : 123 : xyz
3    : 32  : foo
-2.3 : bar : bar

Search and replace

$ perl -pe 's/3/%/' test.txt
abc  : 12% : xyz
%    : 32  : foo
-2.% : bar : bar

$ # use g flag to replace all occurrences, not just first match in line
$ perl -pe 's/3/%/g' test.txt
abc  : 12% : xyz
%    : %2  : foo
-2.% : bar : bar

$ # conditional replacement
$ perl -pe 's/3/@/g if /foo/' test.txt 
abc  : 123 : xyz
@    : @2  : foo
-2.3 : bar : bar

$ # using shell variables
$ r="@"
$ perl -pe "s/3/$r/" test.txt 
abc  : 12@ : xyz
@    : 32  : foo
-2.@ : bar : bar

$ # preferred approach is to use ENV hash variable
$ export s="%"
$ perl -pe 's/3/$ENV{s}/' test.txt 
abc  : 12% : xyz
%    : 32  : foo
-2.% : bar : bar

Search and replace special characters

The \Q and q() constructs are helpful to nullify regex meta characters

$ # if not properly escaped or quoted, it can lead to errors
$ echo '*.^[}' | perl -pe 's/*.^[}/abc/'
Quantifier follows nothing in regex; marked by <-- HERE in m/* <-- HERE .^[}/ at -e line 1.

$ echo '*.^[}' | perl -pe 's/\*\.\^\[}/abc/'
abc

$ echo '*.^[}' | perl -pe 's/\Q*.^[}/abc/'
abc

$ echo '*.^[}' | perl -pe 's/\Q*.^[}/\$abc\$/'
$abc$

$ echo '*.^[}' | perl -pe 's/\Q*.^[}/q($abc$)/e'
$abc$

Print lines based on line number or pattern

$ perl -ne 'print if /a/' test.txt 
abc  : 123 : xyz
-2.3 : bar : bar

$ perl -ne 'print if !/abc/' test.txt 
3    : 32  : foo
-2.3 : bar : bar

$ seq 123 135 | perl -ne 'print if $. == 7'
129

$ seq 1 30 | perl -ne 'print if eof'
30

$ # Use exit to save time on large input files
$ seq 14323 14563435 | perl -ne 'if($. == 234){print; exit}'
14556

$ # length() can also be used instead of length $_
$ seq 8 13 | perl -lne 'print if length $_ == 1'
8
9

Print range of lines based on line number or pattern

$ seq 123 135 | perl -ne 'print if $. >= 3 && $. <= 5'
125
126
127

$ # $. is default variable compared against when using ..
$ seq 123 135 | perl -ne 'print if 3..5'
125
126
127

$ # can use many alternatives, eof looks more readable
$ seq 5 | perl -ne 'print if 3..eof'
3
4
5

$ # matching regex specified by /pattern/ is checked against $_
$ seq 5 | perl -ne 'print if 3../4/'
3
4

$ seq 1 30 | perl -ne 'print if /4/../6/'
4
5
6
14
15
16
24
25
26

$ seq 2 8 | perl -ne 'print if !(/4/../6/)'
2
3
7
8

.. vs ...

$ echo -e '10\n11\n10' | perl -ne 'print if /10/../10/'
10
10

$ echo -e '10\n11\n10' | perl -ne 'print if /10/.../10/'
10
11
10

Column manipulations

$ echo -e "1 3 4\na b c" | perl -nale 'print $F[1]'
3
b

$ echo -e "1,3,4,8\na,b,c,d" | perl -F, -lane 'print $F[$#F]'
8
d

$ perl -F: -lane 'print "$F[0] $F[2]"' test.txt 
abc    xyz
3      foo
-2.3   bar

$ perl -F: -lane '$sum+=$F[1]; END{print $sum}' test.txt 
155

$ perl -F: -lane '$F[2] =~ s/\w(?=\w)/$&,/g; print join ":", @F' test.txt 
abc  : 123 : x,y,z
3    : 32  : f,o,o
-2.3 : bar : b,a,r

$ perl -F'/:\s*[a-z]+/i' -lane 'print $F[0]' test.txt 
abc  : 123 
3    : 32  
-2.3 

$ perl -F'\s*:\s*' -lane 'print join ",", grep {/[a-z]/i} @F' test.txt 
abc,xyz
foo
bar,bar

$ perl -F: -ane 'print if (grep {/\d/} @F) < 2' test.txt 
abc  : 123 : xyz
-2.3 : bar : bar

Dealing with duplicates

$ cat duplicates.txt 
abc 123 ijk
foo 567 xyz
abc 123 ijk
bar 090 pqr
tst 567 zzz

$ # whole line
$ perl -ne 'print if !$seen{$_}++' duplicates.txt 
abc 123 ijk
foo 567 xyz
bar 090 pqr
tst 567 zzz

$ # particular column
$ perl -ane 'print if !$seen{$F[1]}++' duplicates.txt 
abc 123 ijk
foo 567 xyz
bar 090 pqr

Multiline processing

$ # save previous lines to make it easier for multiline matching
$ perl -ne 'print if /3/ && $p =~ /abc/; $p = $_' test.txt 
3    : 32  : foo

$ perl -ne 'print "$p$_" if /3/ && $p =~ /abc/; $p = $_' test.txt 
abc  : 123 : xyz
3    : 32  : foo

$ # with multiline matching, -0777 slurping not advisable for very large files
$ perl -0777 -ne 'print $1 if /.*abc.*\n(.*3.*\n)/' test.txt 
3    : 32  : foo
$ perl -0777 -ne 'print $1 if /(.*abc.*\n.*3.*\n)/' test.txt 
abc  : 123 : xyz
3    : 32  : foo

$ # use s flag to allow .* to match across lines
$ perl -0777 -pe 's/(.*abc.*32)/ABC/s' test.txt 
ABC  : foo
-2.3 : bar : bar

$ # use m flag if ^$ anchors are needed to match individual lines
$ perl -0777 -pe 's/(.*abc.*3)/ABC/s' test.txt 
ABC : bar : bar
$ perl -0777 -pe 's/(.*abc.*^3)/ABC/sm' test.txt 
ABC    : 32  : foo
-2.3 : bar : bar

$ # print multiple lines after matching line
$ perl -ne 'if(/abc/){ print; foreach (1..2){$n = <>; print $n} }' test.txt 
abc  : 123 : xyz
3    : 32  : foo
-2.3 : bar : bar

Using modules

$ echo 'a,b,a,c,d,1,d,c,2,3,1,b' | perl -MList::MoreUtils=uniq -F, -lane 'print join ",",uniq(@F)'
a,b,c,d,1,2,3

$ base64 test.txt 
YWJjICA6IDEyMyA6IHh5egozICAgIDogMzIgIDogZm9vCi0yLjMgOiBiYXIgOiBiYXIK
$ base64 test.txt | base64 -d
abc  : 123 : xyz
3    : 32  : foo
-2.3 : bar : bar
$ base64 test.txt | perl -MMIME::Base64 -ne 'print decode_base64($_)' 
abc  : 123 : xyz
3    : 32  : foo
-2.3 : bar : bar

$ perl -MList::MoreUtils=indexes -nale '@i = indexes { /[a-z]/i } @F if $. == 1; print join ",", @F[@i]' test.txt 
abc,xyz
3,foo
-2.3,bar

In place editing

$ perl -i -pe 's/\d/*/g' test.txt 
$ cat test.txt 
abc  : *** : xyz
*    : **  : foo
-*.* : bar : bar

$ perl -i.bak -pe 's/\*/^/g' test.txt 
$ cat test.txt 
abc  : ^^^ : xyz
^    : ^^  : foo
-^.^ : bar : bar
$ cat test.txt.bak 
abc  : *** : xyz
*    : **  : foo
-*.* : bar : bar

Further Reading

Perl Introduction - Introductory course for Perl 5 through examples
Perl curated resources
Handy Perl regular expressions
What does this regex mean?
Perl one-liners
Perl command line switches
Env

### cut

remove sections from each line of files

For columns operations with well defined delimiters, cut command is handy

Examples

ls -l | cut -d' ' -f1 first column of ls -l
- -d option specifies delimiter character, in this case it is single space character (Default delimiter is TAB character)
- -f option specifies which fields to print separated by commas, in this case field 1
cut -d':' -f1 /etc/passwd prints first column of /etc/passwd file
cut -d':' -f1,7 /etc/passwd prints 1st and 7th column of /etc/passwd file with : character in between
cut -d':' --output-delimiter=' ' -f1,7 /etc/passwd use space as delimiter between 1st and 7th column while printing
cut Q&A on unix stackexchange

### paste

merge lines of files

Examples

paste list1.txt list2.txt list3.txt > combined_list.txt combines the three files column-wise into single file, the entries separated by TAB character
paste -d':' list1.txt list2.txt list3.txt > combined_list.txt the entries are separated by : character instead of TAB
paste Q&A on unix stackexchange

$ # one column to multiple column, denoted by number of -
$ seq 5 | paste - -
1	2
3	4
5	

$ # specifying different output delimiter, default is tab
$ seq 5 | paste -d, - -
1,2
3,4
5,

$ # if number of columns to specify is large, use the printf trick
$ seq 5 | paste $(printf -- "- %.s" {1..3})
1	2	3
4	5	

$ # paste is quite useful to combine all input lines into single line
$ seq 10 | paste -sd,
1,2,3,4,5,6,7,8,9,10

### column

columnate lists

$ cat dishes.txt 
North alootikki baati khichdi makkiroti poha 
South appam bisibelebath dosa koottu sevai 
West dhokla khakhra modak shiro vadapav 
East handoguri litti momo rosgulla shondesh 

$ column -t dishes.txt 
North  alootikki  baati         khichdi  makkiroti  poha
South  appam      bisibelebath  dosa     koottu     sevai
West   dhokla     khakhra       modak    shiro      vadapav
East   handoguri  litti         momo     rosgulla   shondesh

More examples here

### pr

convert text files for printing

$ pr sample.txt 


2016-05-29 11:00                    sample.txt                    Page 1


This is an example of adding text to a new file using cat command.
Press Ctrl+d on a newline to save and quit.
Adding a line of text at end of file

Options include converting text files for printing with header, footer, page numbers, double space a file, combine multiple files column wise, etc
More examples here

$ # single column to multiple column, split vertically
$ # for example, in command below, output of seq is split into two
$ seq 5 | pr -2t
1				    4
2				    5
3

$ # different output delimiter can be used by passing string to -s option
$ seq 5 | pr -2ts' '
1 4
2 5
3

$ # use -a option to split across
$ seq 5 | pr -2ats' : '
1 : 2
3 : 4
5

$ # use $ to expand characters denoted by escape characters like \t for tab
$ seq 5 | pr -3ts$'\t'
1	3	5
2	4

$ # or leave the argument to -s empty as tab is default
$ seq 5 | pr -3ts
1	3	5
2	4

We can use a combination of different commands for complicated operations. For example, transposing a table

$ tr ' ' '\n' < dishes.txt | pr -$(wc -l < dishes.txt)t
North		  South		    West	      East
alootikki	  appam		    dhokla	      handoguri
baati		  bisibelebath  khakhra	      litti
khichdi		  dosa		    modak	      momo
makkiroti	  koottu	    shiro	      rosgulla
poha		  sevai		    vadapav	      shondesh

Notice how pr neatly arranges the columns. If spacing is too much, we can use column

$ tr ' ' '\n' < dishes.txt | pr -$(wc -l < dishes.txt)ts | column -t
North      South         West     East
alootikki  appam         dhokla   handoguri
baati      bisibelebath  khakhra  litti
khichdi    dosa          modak    momo
makkiroti  koottu        shiro    rosgulla
poha       sevai         vadapav  shondesh

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Text_Processing.md

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Text Processing

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Text Processing