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In many scripts in my organisation and even on online tutorials, this is a common if clause I come across :

if [ $# -eq "somethng" -o $# -eq "somethng" ]

what does this $# condition match—some user input by default?
Can this be used on command line directly too??

Timo
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NoobEditor
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  • In bash, see Special Parameters (pp. 8-9) and their expansion (pp. 19...) and finally Conditional Expressions (pp. 28-29) for context. –  Feb 12 '14 at 19:11
  • Things like $# are unfortunately difficult to find in the bash documentation. See this question. – Keith Thompson Feb 12 '14 at 19:36
  • @KeithThompson : wow...u just gave me a bang-on ref url!!! :D – NoobEditor Feb 12 '14 at 19:38
  • @KeithThompson I printed the bash manual in booklet form using the livre script. A printed version makes a huge difference for me in this context. As is finding an answer like the one you link to which provides the exact terminology for the concepts at hand. –  Feb 12 '14 at 21:39
  • @KeithThompson Also newbie here. But IMHO, $ and # should not appear together in the list on special parameters as conceptually expansion should not be confused with the parameters themselves. Contrary to what I read sometimes $ has nothing to do with variables. As you know it expands a parameter, a variable or enables command substitution or arithmetic expansion. There is an entire section about expansion, including of parameters, with examples. Variable is never defined; "word" and "name" are. Prefixing the params with $ would mean prefixing the shell variables in the next section too... –  Feb 13 '14 at 01:35
  • Actually saying a variable was not defined was wrong as it is defined as a "parameter denoted by a name". But expansion remains unrelated is what I mean here. Anyways, reading this entirely helps but surely it could be more searchable. Maybe there's a way that searching for "$#" could land you in the special params section without having to modify the text. –  Feb 13 '14 at 03:37
  • Also related: What does $# mean in shell? – G-Man Says 'Reinstate Monica' Nov 25 '18 at 20:54

1 Answers1

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$# is number of arguments you passed to bash script, not counting $0, which is program name.

Example:

#!/bin/bash

echo "Number of arguments is: $#"

Then run:

% cuonglm at ~
% ./test.sh a b c d
Number of arguments is: 4
cuonglm
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