build: fix building manpages on systems where asciidoc is already installed #169
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…talled It doesn't really make sense to run one command that isn't installed, to see if another command is installed. Even though I have a2x installed, the build fails with: ``` make: Entering directory '/var/tmp/portage/dev-vcs/git-absorb-0.7.0/work/git-absorb-0.7.0/Documentation' make: which: No such file or directory Makefile:4: *** "No a2x in PATH; install asciidoc.". Stop. ``` The "which" utility is not guaranteed to be installed either, and if it is, its behavior is not portable either. This means that when various programs are installed, the `which` check will report a fatal error because the which tool did not exist and the shell returned a nonzero status when attempting to fork+exec. If it did exist, it might not be an implementation of `which` that returns nonzero when commands do not exist. The general scripting suggestion is to use the "command -v" shell builtin; this is required to exist in all POSIX 2008 compliant shells, and is thus guaranteed to work everywhere. For some in-depth discussions on the topic, see: - https://mywiki.wooledge.org/BashFAQ/081 - https://unix.stackexchange.com/questions/85249/why-not-use-which-what-to-use-then/85250#85250 Examples of open-source shells likely to be installed as /bin/sh on Linux, which implement the 15-year-old standard: ash, bash, busybox, dash, ksh, mksh and zsh. Several Linux distros which *do* currently ship a (decent quality) `which` utility in their default install are looking to get rid of it: - Gentoo: https://bugs.gentoo.org/646588 - Debian: https://lwn.net/Articles/874049/
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doc fail to build if 'which' utility not installed, replace it with the built-in shell 'command'. Link: tummychow/git-absorb#169 Closes: https://bugs.gentoo.org/951208 Signed-off-by: Yixun Lan <dlan@gentoo.org>
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It doesn't really make sense to run one command that isn't installed, to see if another command is installed. Even though I have a2x installed, the build fails with:
The "which" utility is not guaranteed to be installed either, and if it is, its behavior is not portable either. This means that when various programs are installed, the
whichcheck will report a fatal error because the which tool did not exist and the shell returned a nonzero status when attempting to fork+exec. If it did exist, it might not be an implementation ofwhichthat returns nonzero when commands do not exist.The general scripting suggestion is to use the "command -v" shell builtin; this is required to exist in all POSIX 2008 compliant shells, and is thus guaranteed to work everywhere.
For some in-depth discussions on the topic, see:
Examples of open-source shells likely to be installed as /bin/sh on Linux, which implement the 15-year-old standard: ash, bash, busybox, dash, ksh, mksh and zsh.
Several Linux distros which do currently ship a (decent quality)
whichutility in their default install are looking to get rid of it: