Shell scripting: test if a string contains a character (including chars like '*' and '\') [duplicate]

Question

In a shell script, I have a function afun that was passed a few arguments. I need another function that will help me find out if at least one of those arguments contains a given character which is not known a priori (but it could be any character like a, 9, *, \, |, /, (, [ and so on, but not space):

afun() {
  # Some commands here...
  testchar=... # here I have some logic which decides what character should be tested below
  # Now, call another function to test if any of the args to "afun"
  # contain the character in var "testchar".
  # If it does, print "Found character '$testchar' !"
}

The proposed function should be compatible at least with Bash, Dash, Ash and ZSH - because I have a script that needs to run under different Linux distros (Ubuntu, Alpine Linux) installed in Docker containers, and I don't want to declare a dependency on a specific shell interpreter since not all those containers will necessarily have it installed.

Bash, Dash, Ash and ZSH . That sounds like you're kidding. ;) And the question is not very clear.. — sjsam
– sjsam, Commented Jun 17, 2016 at 18:48
ZSH has more features than Ash, but is it unreasonable what I'm asking? And thanks, I've fixed the variable name (it should be testchar instead of c) — Elifarley
– Elifarley, Commented Jun 17, 2016 at 18:50
@Elifarley, it's not just "more features" -- ash, bash and ksh are compliant with POSIX sh (barring caveats like bash's support for echo -e), whereas zsh is intentionally incompatible with the standard (in places where its maintainers decided -- with some basis in fact -- that the standard enforces bad design decisions) unless running in non-default posix mode. That's not to say that writing scripts compatible with both zsh and POSIX-compliant shells can't be done, but it does mean that it requires a bit more care than the usual (ash+bash+ksh) practice of just complying with POSIX. — Charles Duffy
– Charles Duffy, Commented Jun 17, 2016 at 19:23
BTW, local is not defined by POSIX -- if you're going for maximal compatibility, you'll want to do without. — Charles Duffy
– Charles Duffy, Commented Jun 17, 2016 at 19:26

Elifarley · Accepted Answer · 2016-06-20 14:15:33Z

4

Here's my proposed shell function:

charexists() {
  char="$1"; shift
  case "$*" in *"$char"*) return;; esac; return 1
}

And here's how you can use it:

afun() {
  # Some commands here...
  testchar=... # here I have some logic which decides what character should be tested below
  # Now, call another function to test if any of the args to "afun"
  # contain the character in var "testchar".
  # If it does, print "Found character '$testchar' !"
  charexists "$testchar" "$@" && echo "Found character '$testchar' !"
}

Here's a simple unit test:

fun2test=charexists
{ $fun2test '*' 'a*b' && printf 1 ;} ; \
{ $fun2test '*' 'a' '*' '\' 'b#c|+' '\' && printf 2 ;} ;\
{ $fun2test '\' 'a' '*' '\' 'b#c|+' '\' && printf 3 ;} ;\
{ $fun2test '*' 'ab' || printf 4 ;} ; \
{ $fun2test '*' 'a' '' '/' 'b#c|+' '\' || printf 5 ;}; echo

It should print 12345 if all 5 tests pass.

I have just tested under Bash, Dash, Ash and ZSH and all went well.

edited Jun 20, 2016 at 14:15

answered Jun 17, 2016 at 19:07

Elifarley

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2 Comments

Charles Duffy Over a year ago

charexists "$testchar" $* -- without the $* quoted -- will behave badly if your list of arguments contains, say, * -- unless you want that to be expanded to a list of filenames in the current directory.

Elifarley Over a year ago

Indeed! Fixed, thanks!

sjsam · Accepted Answer · 2016-06-17 18:58:45Z

-1

Below is my bash specific solution for this :

#!/bin/bash
fun()
{
  not_allowed=' ' # Charater which is not allowed
  [[ "$1" =~ $not_allowed ]] && echo "Character which is not allowed found"
}

fun "TestWithoutSpace"
fun "Test with space"

answered Jun 17, 2016 at 18:58

sjsam

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1 Comment

Elifarley Over a year ago

Using the test case found in my solution, your proposed solution only prints 34, so it fails the first 2 tests.

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