Bash – What do square brackets in bash case statement mean

bashdocumentation

case word in [ [(] pattern [| pattern]...) command-list ;;]... esac

What are square brackets indicating? Other websites omit them (i.e. no [[(] etc.)

http://www.thegeekstuff.com/2010/07/bash-case-statement/ shows this:
no use of [[(] etc.

case expression in
    pattern1 )
        statements ;;
    pattern2 )
        statements ;;
    ...
esac

Thanks for the detailed responses below. I am extremely appreciative of the clarification.

Best Answer

Read the authoritative source: the GNU bash manual
https://www.gnu.org/software/bash/manual/bashref.html#Conditional-Constructs

The square brackets indicate optional stuff.

The only mandatory parts are: case word in esac -- this is valid bash that happens to do nothing.

Related Solutions

Bash – Left and right square brackets treated differently by sed/bash

[ introduces a character class and ] closes it.

If sed sees only ] (i.e. the closing command), it will be OK, sed assumes this is not special command.

Using only [ (without a closing ]) confuses sed, so it must be escaped.

On a side note, there is no need for

g (global) flag (only one substitution per line)
escape [ in replacement.

I managed your change with

sed -e "s/]/']/" -e "s/\[/['/"

FreeBSD – Using Double Square Brackets in Bash

The [[ syntax is a ksh and bash thing and is not present in all shells. Your FreeBSD default shell is probably sh (or bash acting like sh), not bash. The equivalent syntax that should work on all shells is:

case $1 in
        *[/\\] ) echo "Yes";;
esac

Best Answer

Related Solutions

Bash – Left and right square brackets treated differently by sed/bash

FreeBSD – Using Double Square Brackets in Bash

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