CODEWITHSUNDEEP
shell
user2352151
user2352151

Reputation: 81

What is the meaning of ${var#?} in a shell script

I don't kanow what #? mean, I goolged,found nothing

the full file: tinode/chat

goplat=( darwin windows linux )
# Supported CPU architectures: amd64
goarc=( amd64 )
# Supported database tags
dbtags=( mysql mongodb rethinkdb )

for line in $@; do
  eval "$line"
done

version=${tag#?}

if [ -z "$version" ]; then
  # Get last git tag as release version. Tag looks like 'v.1.2.3', so strip 'v'.
  version=`git describe --tags`
  version=${version#?}
fi

Upvotes: 0

Views: 1287

Answers (2)

Keith Thompson
Keith Thompson

Reputation: 263267

${tag#?} expands to the value of $tag with the first character deleted.

Quoting the POSIX shell specification:

${parameter#[word]}
Remove Smallest Prefix Pattern. The word shall be expanded to produce a pattern. The parameter expansion shall then result in parameter, with the smallest portion of the prefix matched by the pattern deleted. If present, word shall not begin with an unquoted '#'.

In this case the pattern is ?, which matches a single character.

If you're using bash, the Bash manual also covers this (you can view the manual on your system with info bash):

'${PARAMETER#WORD}'
'${PARAMETER##WORD}'
     The WORD is expanded to produce a pattern just as in filename
     expansion (*note Filename Expansion::).  If the pattern matches the
     beginning of the expanded value of PARAMETER, then the result of
     the expansion is the expanded value of PARAMETER with the shortest
     matching pattern (the '#' case) or the longest matching pattern
     (the '##' case) deleted.  If PARAMETER is '@' or '*', the pattern
     removal operation is applied to each positional parameter in turn,
     and the expansion is the resultant list.  If PARAMETER is an array
     variable subscripted with '@' or '*', the pattern removal operation
     is applied to each member of the array in turn, and the expansion
     is the resultant list.

Upvotes: 4

user2352151
user2352151

Reputation: 81

#!/bin/bash
tag='123'
version=${tag#?}
echo ${version}  # output is: 23

=======
so #? is remove first character?

Upvotes: -2

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