Shell - automatically trim

 

zzh@ZZHPC:~$ a="    aaa    aaa    "
zzh@ZZHPC:~$ echo "$a"
    aaa    aaa    
zzh@ZZHPC:~$ echo $a
aaa aaa
zzh@ZZHPC:~$ b="bbb${a}bbb"
zzh@ZZHPC:~$ echo "$b"
bbb    aaa    aaa    bbb
zzh@ZZHPC:~$ echo $b
bbb aaa aaa bbb
zzh@ZZHPC:~$ c="ccc ${a} ccc"
zzh@ZZHPC:~$ echo "$c"
ccc     aaa    aaa     ccc
zzh@ZZHPC:~$ echo $c
ccc aaa aaa ccc
zzh@ZZHPC:~$ d="ddd    ${a}    ddd"
zzh@ZZHPC:~$ echo "$d"
ddd        aaa    aaa        ddd
zzh@ZZHPC:~$ echo  $d
ddd aaa aaa ddd

Shell will trim leading and trailing space or tab characters and also squeeze sequences of tabs and spaces into a single space when assigning a string to a variable.

zzh@ZZHPC:~$ echo "   aaa   " > aaa.txt
zzh@ZZHPC:~$ cat aaa.txt
   aaa   

zzh@ZZHPC:~$ cat aaa.sh
while read line
do
    echo $line
    echo "$line"
    echo "bbb${line}bbb"
done < aaa.txt

zzh@ZZHPC:~$ ./aaa.sh
aaa
aaa
bbbaaabbb