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Written: 05-Mar-2022
Chaining commands is where shell becomes very handy. This is
particularly useful for doing stuff on a single line - called one liners
cleverly - on the console. There are several techniques for this, and
best explained with an example: cmd1 operator
cmd2 Replacing operator with the following
yields different results.
; - Simple chain - do cmd1 then do
cmd2.&& - AND - do cmd1 and if
successful do cmd2.|| - OR - do cmd1 and if unsuccessful do
cmd2.| - Pipe - do cmd1 and input the results
to cmd2&& and ; are pretty similar,
however if cmd1 returns an error then with
&& the next command won’t run. Geeks
for geeks has more info (as always).
The first three are pretty obvious, however piping - | -
is very tasty. The functionality allows the output of one command to be
the input of another. A simple example of this would be:
ls | grep ".py"Which would find any python files in the current directory.
As an aside piping ls into grep isn’t
ideal1 and find should be used
instead (but I’ve done it many times, just don’t let anyone see 🙈). An
example I’ve used recently is:
find . -iregex '.*\.jpg' | fim -This searches for jpeg images in the current folder
using find (ignoring all the arguments etc.) and them
passes them to fim to view. Notably the - is
what tells fim to look for input from something else, but
not all programs require it (like grep above). Look at the
man page for help here.
The mechanism of how this works is called standard
streams (you may hear of stdin and stdout)
but it’s not required info for a quick and dirty understanding.
Terminal Tut 1 - Meta Commands