Shell Programming and Scripting

#!/usr/bin/env bash

# @(#) s3       Demonstrate remove files in groups, xargs.

# Utility functions: print-as-echo, print-line-with-visual-space, debug.
# export PATH="/usr/local/bin:/usr/bin:/bin"
LC_ALL=C ; LANG=C ; export LC_ALL LANG
pe() { for _i;do printf "%s" "$_i";done; printf "\n"; }
pl() { pe;pe "-----" ;pe "$*"; }
em() { pe "$*" >&2 ; }
db() { ( printf " db, ";for _i;do printf "%s" "$_i";done;printf "\n" ) >&2 ; }
db() { : ; }
C=$HOME/bin/context && [ -f $C ] && $C /bin/ls xargs tr

# Remove debris from previous runs.

FILE=${1-data2}

# Create a number of files.

pl " Temporary files:"
rm -f t*
touch t{1..9}
/bin/ls t*

# Put temporary files into a list.
/bin/ls -1 t* > $FILE

pl " Input data file $FILE, columnized:"
column $FILE

pl " Results, xargs, default command is echo:"
xargs < $FILE

pl " Files are still present:"
/bin/ls t*
echo " Exit status from ls: $?"

pl " Results, change command to rm, files are now gone, expect message:"
xargs rm < $FILE
/bin/ls t*
echo " Exit status from ls: $?"

# Now with a file with a special character -- a space -- in it.
pl " Temporary files:"
rm -f t*
touch t{1..9} "t 10"
/bin/ls t*

pl " Results, not all files are gone:"
xargs rm < $FILE
/bin/ls t*
echo " Exit status from ls: $?"

# Again with a file with a special character -- a space -- in it.
pl " Temporary files:"
rm -f t*
touch t{1..9} "t 10"
/bin/ls t*

pl " List files with quotes around them, (displayed columnized):"
/bin/ls -Q t* |
tee $FILE |
column

pl " Results, files are now gone, expect message:"
xargs rm < $FILE
/bin/ls t*
echo " Exit status from ls: $?"

# Third time, with a file with a special character -- a space -- in it.
pl " Temporary files:"
rm -f t*
touch t{1..9} "t 10"
/bin/ls t*

pl " Add a null character to the end of each name:"
/bin/ls -1 t* |
tr '\n' '\0' |
tee $FILE 

pl " Results, files are now gone, expect message:"
xargs --null rm < $FILE
/bin/ls t*
echo " Exit status from ls: $?"

exit 0

$ ./s3

Environment: LC_ALL = C, LANG = C
(Versions displayed with local utility "version")
OS, ker|rel, machine: Linux, 3.16.0-4-amd64, x86_64
Distribution        : Debian 8.6 (jessie) 
bash GNU bash 4.3.30
/bin/ls ls (GNU coreutils) 8.23
xargs (GNU findutils) 4.4.2
tr (GNU coreutils) 8.23

-----
 Temporary files:
t1  t2  t3  t4  t5  t6  t7  t8  t9

-----
 Input data file data2, columnized:
t1      t2      t3      t4      t5      t6      t7      t8      t9

-----
 Results, xargs, default command is echo:
t1 t2 t3 t4 t5 t6 t7 t8 t9

-----
 Files are still present:
t1  t2  t3  t4  t5  t6  t7  t8  t9
 Exit status from ls: 0

-----
 Results, change command to rm, files are now gone, expect message:
/bin/ls: cannot access t*: No such file or directory
 Exit status from ls: 2

-----
 Temporary files:
t 10  t1  t2  t3  t4  t5  t6  t7  t8  t9

-----
 Results, not all files are gone:
t 10
 Exit status from ls: 0

-----
 Temporary files:
t 10  t1  t2  t3  t4  t5  t6  t7  t8  t9

-----
 List files with quotes around them, (displayed columnized):
"t 10"  "t1"    "t2"    "t3"    "t4"    "t5"    "t6"    "t7"    "t8"    "t9"

-----
 Results, files are now gone, expect message:
/bin/ls: cannot access t*: No such file or directory
 Exit status from ls: 2

-----
 Temporary files:
t 10  t1  t2  t3  t4  t5  t6  t7  t8  t9

-----
 Add a null character to the end of each name:
t 10t1t2t3t4t5t6t7t8t9
-----
 Results, files are now gone, expect message:
/bin/ls: cannot access t*: No such file or directory
 Exit status from ls: 2