Check array entry for string value (mostly a syntax error)

Question

I'm stuck in a syntax lack; tried multiple ways but I somehow don't see the solution. I'm sure it's super simple, but I currently just don't get it.

Goal

Split the QUEUE_STRING into 2 parameters, check the first for equality with one of 2 strings, add the second in another commandline call

What I've got so far

#!/bin/sh
QUERY_STRING="setSize&10240000"
arr=${QUERY_STRING//&/ }
if [ $arr[0] = "status" ]; then
      echo "YES"
      ./myApp status
elif [ $arr[0] = "setSize" ] ; then
      echo "NO"
      ./myApp setSize $arr[1]
else 
      echo "ERROR"
fi

I just get "error" but I should receive "NO"

Thanks for your help

learn to use set -x (usually )right after the first line, so you actually see what your script is doing when executing it. This will always give you an insight on what might be wrong. — Ron
– Ron, Commented Sep 17, 2020 at 14:34

Ron · Accepted Answer · 2020-09-17 14:55:08Z

2

Here you go:

#!/bin/bash
set -x # you can comment off this line to disable debug output
QUERY_STRING="setSize&10240000"
arr=(${QUERY_STRING//&/ })
if [ "{$arr[0]}" = "status" ]; then
      echo "YES"
      ./myApp status
elif [ "${arr[0]}" = "setSize" ] ; then
      echo "NO"
      ./myApp setSize $arr[1]
else
      echo "ERROR"
fi

Edit

Here it is in sh

#!/bin/sh
set -x # you can comment off this line to disable debug output
QUERY_STRING="setSize&10240000"
arr=$(echo "$QUERY_STRING"|cut -d\& -f 1)
if [ "$arr" = "status" ]; then
      echo "YES"
      ./myApp status
elif [ "$arr" = "setSize" ] ; then
      echo "NO"
      ./myApp setSize "$(echo "$QUERY_STRING"|cut -d\& -f 2)"
else
      echo "ERROR"
fi

edited Sep 17, 2020 at 14:55

answered Sep 17, 2020 at 14:37

Ron

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4 Comments

Human_BetaRelease Over a year ago

Thanks, unfortunally /bin/bash is not available on my system (and can't be added). With /bin/sh it unfortunally doesn't work; complains about "unexpected (" in line 4

Ron Over a year ago

it does work in Bash, it will hardly work in sh

Human_BetaRelease Over a year ago

Saw your comment too late, edited mine. I can't work with bash, I need sh

glenn jackman Over a year ago

You're leaving yourself open to filename expansion: QUERY_STRING="foo&*"; arr=(${QUERY_STRING//&/ }); declare -p arr -- turn off filename expansion before defining the array with set -f

dash-o · Accepted Answer · 2020-09-17 14:40:58Z

0

The posted code assumes 'arr' is an array, is tries to access the 0-th element using $arr[0]. Both are coded incorrectly, and need to be fixed.

The assignment to arr should create an array. This can be done with "read -a"

read -a arr <<< "${QUERY_STRING//&/ }"

The check for the first element should use "${arr[0]}" and not $arr[0]:

if [ "${arr[0]}" = "status" ]; then
      echo "YES"
      ./myApp status
...

answered Sep 17, 2020 at 14:40

dash-o

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1 Comment

Human_BetaRelease Over a year ago

I unfortunally get a "./mq: line 5: syntax error: unexpected redirection" for read -a, as this is a bash function as well. I cannot use bash; POSIX sh is required

glenn jackman · Accepted Answer · 2020-09-17 15:22:49Z

0

Splitting strings in shell is a fairly common idiom: use IFS and read:

If you're using bash, use a here-string:

IFS='&' read -r key value <<<"$QUERY_STRING"

If you want portability or you're using a plain POSIX shell, use a here-doc:

IFS='&' read -r key value <<END_INPUT
$QUERY_STRING
END_INPUT

Alternately, parameter substitition:

key=${QUERY_STRING%%&*}   # remove the longest suffix starting with '&'
value=${QUERY_STRING#*&}  # remove the shortest prefix ending with '&'

then a case statement is more compact than a cascading if

case "$key" in
  status)  echo YES; ;;
  setSize) echo NO; echo "$value" ;;
  *)       echo ERROR ;;
esac

NO
10240000

edited Sep 17, 2020 at 15:22

answered Sep 17, 2020 at 15:13

glenn jackman

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