linux - why is this variable not being changed? -

this question has answer here:

• assign value variable in loop 1 answer

i have larger script smaller 1 shows problem:

#!/bin/bash x=0 if [[ $x == 0 ]]    ls | while read l         x=5      echo "this file $l , set 5 --> $x"    done fi echo "this should not 0 --> $x"  

if variable set outside while loop works expect. bash version 3.2.25(1)-release (x86_64-redhat-linux-gnu). i'll feel dumb if obvious thing.

the x being set 5 in sub-shell (because part of pipeline), , happens in sub-shell not affect parent shell.

you can avoid sub-shell , result expected using process substitution in bash:

#!/bin/bash x=0 if [[ $x == 0 ]]    while read l         x=5      echo "this file $l , set 5 --> $x"    done < <(ls) fi echo "this should not 0 --> $x" 

now while loop part of main shell process (only ls in sub-process) variable x affected.

we can discuss merits of parsing output of ls time; largely incidental issue in question.

another option be:

#!/bin/bash x=0 if [[ $x == 0 ]]    ls |     {    while read l         x=5      echo "this file $l , set 5 --> $x"    done    echo "this should not 0 --> $x"    } fi echo "this should 0 still, though --> $x"