[SOLVED] (BASH) Looping over an array

Dick Dastardly · 01-18-2012, 12:02 AM

Some more variable stuff i'm afraid!

Is it possible to loop over an array (i think that's what it's called) and act on a specific variable?

For example, i would like to find all variables that DO NOT have XXX in it and append ZZZ to them.

Code:

_var=(1 2 3 4XXX)
echo ${_var[@]}|grep -v "XXX"

Doesn't seem to work and I can't get a for loop to either.
Can anyone prod me in the right direction?
Thanks muchly

xylos · 01-18-2012, 01:05 AM

Something along these lines (assuming it's not a sparse array):

Code:

ARRAY=( 1 2 3 4XXX )
declare -i MAXNUMBER=5
declare -i LOOPCONTROL=0
while [ $LOOPCONTROL -lt $MAXNUMBER ]; do
   if [ `echo ${ARRAY[$LOOPCONTROL]} | grep -c "XXX"` -ne 0 ]; then
      TEMPVALUE=`echo ${ARRAY[$LOOPCONTROL]}`
      ARRAY[$LOOPCONTROL]="$TEMPVALUE""ZZZ"                       # Edited to change this to ZZZ instead of XXX as per OP
   fi
done

Just off the top of my head... haven't tried it on a box (stuck on a Windows machine at the moment), but that should do what you're looking for (in horribly inefficient but hopefully very readable syntax).

grail · 01-18-2012, 03:24 AM

How about:

Code:

#!/bin/bash

_var=(1 2 3 4XXX)

for i in ${!_var[*]}
do
	[[ ${_var[i]} =~ XXX ]] || _var[i]+=ZZZ
done

printf "%s\n" "${_var[@]}"

Nominal Animal · 01-18-2012, 03:32 AM

Quote:

Originally Posted by Dick Dastardly

For example, i would like to find all variables that DO NOT have XXX in it and append ZZZ to them.

Usually it is easiest to first copy the array to a temporary variable, and rebuild a new array in a loop. You can also use Bash string manipulation to see if the string contains a fixed substring (or glob pattern):

Code:

original=(1 2 3 4XXX)

temporary=("${original[@]}")
original=()
for one in "${temporary[@]}" ; do
    if [ "$one" = "${one/XXX/}" ]; then
        one="${one}ZZZ"
    fi
    original=("${original[@]}" "${one}")
done
unset temporary

echo "${original[@]}"

will yield

Code:

1ZZZ 2ZZZ 3ZZZ 4XXX

The if clause verifies that you cannot remove XXX from the string. (If the string equals the same string with XXX removed, the string does not contain XXX, and therefore we append ZZZ to it.)

Dick Dastardly · 01-18-2012, 03:36 PM

Thanks for the help guys. I'll have a look at this later tonight. =]

Dick Dastardly · 01-21-2012, 09:35 PM

@Nominal Animal suggestion worked for me. Thank you for the help.

2 questions with that code:
1) What does the "original=()" do?
2) What do the slashes do in the if test "if [ "$one" = "${one/XXX/}" ]; then"?
Thanks.

Nominal Animal · 01-22-2012, 07:37 AM

Quote:

Originally Posted by Dick Dastardly

1) What does the "original=()" do?

It sets original to an empty array.

Quote:

Originally Posted by Dick Dastardly

2) What do the slashes do in the if test "if [ "$one" = "${one/XXX/}" ]; then"?

It is a string operation, described in detail in the Bash Reference Manual (Shell Parameter Expansion chapter).

Put simply, ${variable/pattern/replacement} evaluates to the value of variable but with the first pattern replaced by replacement.

There are other similar expressions explained in the link above. For example, ${variable//pattern/replacement} evaluates to the value of variable but all patterns replaced by replacement.

Note that the pattern is actually a glob pattern, similar to the patterns you use to specify file name patterns. Its syntax is explained in the Pattern Matching section in the Bash Reference Manual.

It is easy confuse these glob pattern string expressions with regular expressions, which look similar, but have different special characters. It is a good thing you asked.