How (or why) does this bash script snippet work?
Anthony R Fletcher
arif at mail.nih.gov
Thu Jan 12 19:13:53 UTC 2012
On 12 Jan 2012 at 14:02:50, Dean S. Messing wrote:
>
> In a system script I find this snippet
>
> nodevs=$(< /proc/filesystems fgrep rootfs)
>
> and don't understand the syntax. According to the bash man page,
>
> $(< file) is shorthand for $(cat file). But then the above should read
>
> nodevs=$(< /proc/filesystems | fgrep rootfs)
>
> However, the latter leaves $nodevs empty whereas the former puts the
> stuff that fgrep processes into nodevs as it should.
The command
< /proc/filesystems fgrep rootfs
redirects the input from the file /proc/filesystems into the command
"fgrep rootfs". You could rewrite this as
fgrep rootfs < /proc/filesystems
nodevs=$( command ) takes the result of the command inside the
parentheses and assigns into the variable nodevs.
Anthony.
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