I just want to check if one parameter was supplied in my bash script or not.
I found this, but all the solutions seem to be unnecessarily complicated.
What's a simple solution to this simple problem that would make sense to a beginner?
- ^answers from above possible duplicate are similar to the ones posted here including a comment about using the [[ -z ]] testpd12– pd122016-01-11 21:53:22 +00:00Commented Jan 11, 2016 at 21:53
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3 Answers
Use $# which is equal to the number of arguments supplied, e.g.:
if [ "$#" -ne 1 ] then echo "Usage: ..." exit 1 fi Word of caution: Note that inside a function this will equal the number of arguments supplied to the function rather than the script.
EDIT: As pointed out by SiegeX in bash you can also use arithmetic expressions in (( ... )). This can be used like this:
if (( $# != 1 )) then echo "Usage: ..." exit 1 fi 
3 Comments
SiegeX
since this is
bash question I would suggest if (( $# != 1 ))
tripleee
For a range, a
case statement may be more idiomatic. The syntax looks alien to beginners, though. case $# in [123]) ;; *) echo fail >&2; exit 1;; esac
Adam Zalcman
Expressions in
[] use <, >, != and == for string comparisons and -lt, -gt, -le, -ge, -ne and -eq for arithmetic comparisons. Expressions in (()) use <, >, != and == for arithmetic comparisons. For more operators see bash manpage.The accepted solution checks whether parameters were set by testing against the count of parameters given. If this is not the desired check, that is, if you want to check instead whether a specific parameter was set, the following would do it:
for i in "$@" ; do if [[ $i == "check parameter" ]] ; then echo "Is set!" break fi done Or, more compactly:
for i in "$@" ; do [[ $i == "check argument" ]] && echo "Is set!" && break ; done 
3 Comments
gniourf_gniourf
I'm not sure your method is correct… for example:
./script check parameter will succeed (which is incorrect).
h7r
@gniourf_gniourf You are fully right. I edited with a solution that actually does the trick. Unfortunatelly with a loop.
if (( "$#" != 1 )) then echo "Usage Info:…" exit 1 fi 
2 Comments
jaypal singh
Thanks @SiegeX .. have updated the answer. Out of curiosity, any particular difference I should be aware of?
SiegeX
Only that it supports superior syntax such as
== != < > <= >= and it can also do boolean logic inside a single (( )) much like you can do in C