Grep для строки со списком файлов как источник

Я переписал этот ответ, поскольку он поднял некоторые вопросы, ответы, к которым были немного туманными. Я надеюсь, что этот ответ очищает часть вуали...

Примечание: Использование xargs подходит для передачи позиционных параметров (args) к программе, когда существует столько args, что они превысили бы память, доступную командной строке...

Примечания находятся в сценарии.

#!/bin/bash

  rm -f "/tmp/file   "*

# Create some dummy test files and write their names to /tmp/list
  for x in {A..D} ;do 
      echo "text-$x" >"/tmp/file   $x"
      echo "/tmp/file   $x"
  done >"/tmp/list"

# Set up Quirk 1... with an escaped char \A in the file-name.
        # Replace one of the file-names in the list with a quirky but valid one.
          echo 'quirk 1. \A in filename' >'/tmp/file   \A'
          sed -i 's/A/\\A/'  "/tmp/list"

        # The next two lines show  that 
        #            'file   \A' is in the list      and DOES exist.
        #            'file   A'  is NOT in the list, but DOES exist.
        # Therefore, 'file   A'  should NOT produce a 'grep' match
          echo "Quirk 1. backslash in file-name"  
          echo "   ls:"; ls -1 '/tmp/file   '*A    |nl  
          echo " list:"; sed -n '/A/p' "/tmp/list" |nl
          echo "===================="

# Set up Quirk 2... with $D in the file name
        # Replace one of the file-names in the list with a quirky but valid one.
          echo 'quirk 2. $D in filename' >'/tmp/file   $D'
          sed -i 's/D/\$D/'  "/tmp/list"
          D='D' 
        # The next two lines show  that 
        #            'file   $D' is in the list      and DOES exist.
        #            'file   D'  is NOT in the list, but DOES exist.
          echo "Quirk 2. var \$D=$D in file-name"  
          echo "   ls:"; ls -1 '/tmp/file   '*D    |nl  
          echo " list:"; sed -n '/D/p' "/tmp/list" |nl
          echo "===================="

# The regex search pattern
  regex='(A|C|D)'

# Read lines of a file, and use them as positional parameters.
#  Note: 'protection' means protected from bash pre-processing. (eg path expansion) 
# ============================================================
  ###  
  echo 
  echo "========================================"
  echo "Passing parameters to 'grep' via 'xargs'"    
  echo "========================================"
  echo 
  ###
    echo "# Use 'xargs' with the assumption that every file name contains no meta characters."
    echo "# The result is that file names which contain meta characters, FAILS."   
    echo "# So it interprets '\A' as 'A' and whitespace as a delimiter!"
      <"/tmp/list" xargs  grep -E -H "$regex" 
      echo =====; echo "ERROR: All files in the sample list FAIL!" 
      echo =====; echo
  ###  
    echo "# Use xargs -I{} to avoid problems of whitespace in filenames"
    echo "# But the args are further interpreted by bash, as in escape '\' expansion."
    echo "# Bash still interprets xarg's '\A' as 'A' and so 'grep' processes the wrong file"
    echo "# However the -I{} does protect the $D from var expansion"
      <"/tmp/list" xargs -I{} grep -E -H "$regex" {}
      echo =====; echo "ERROR: The 1st line refers to 'file   A' which is NOT in the list!" 
      echo =====; echo
  ###  
    echo "# Use xargs -0 to avoid problems of whitespace in filenames"
    echo "# 'xargs -0' goes further with parameter protection than -I." 
    echo "# Quotes and backslash are not special (every character is taken literally)" 
      <"/tmp/list" tr '\n' '\0' |xargs -0 grep -E -H "$regex"
      echo  ==; echo "OK" 
      echo  ==; echo
  ###
  echo "====================================="
  echo "Passing parameters directly to 'grep'"    
  echo "====================================="
  echo 
  ###
    echo "# Use 'grep' with the assumption that every file name contains no meta characters."    
    echo "# The result is that file names which contain meta characters, FAILS."   
      grep -E -H "$regex" $(cat "/tmp/list") 
      echo =====; echo "ERROR: All files in the sample list FAIL!" 
      echo =====; echo
  ###  
    echo '# Set bash positional parameters "$1" "$2" ... "$n"'  
    echo "# Note: destructive... original parameters are overwritten"
    echo '#   and, you may need to reset $IFS to its original value'
    IFS=$'\n'
    set $(cat "/tmp/list") 
    grep -E "$regex" "$@"
      echo  ==; echo "OK" 
      echo  ==; echo
  ###
    echo '# Set bash positional parameters "$1" "$2" ... "$n"'  
    echo '# Note: non-destructive... original parameters are not overwritten' 
    echo '# Variable set in the sub-shell are NOT accessible on return.'
    echo '# There is no need to reset $IFS'
    ( IFS=$'\n'
      set $(cat "/tmp/list") 
      grep -E "$regex" "$@" )
      echo  ==; echo "OK" 
      echo  ==; echo
  ### 
    echo '# Using bash array elements "${list[0]}" "${list[1]}" ... "${list[n-1]}"'
    echo '# Note: you may need to reset $IFS to its original value'
    IFS=$'\n'
    list=($(cat "/tmp/list")) 
    grep -E "$regex" "${list[@]}"
      echo  ==; echo "OK" 
      echo  ==; echo
  ### 

Вот вывод

Quirk 1. backslash in file-name
   ls:
     1  /tmp/file   A
     2  /tmp/file   \A
 list:
     1  /tmp/file   \A
====================
Quirk 2. var $D=D in file-name
   ls:
     1  /tmp/file   D
     2  /tmp/file   $D
 list:
     1  /tmp/file   $D
====================

========================================
Passing parameters to 'grep' via 'xargs'
========================================

# Use 'xargs' with the assumption that every file name contains no meta characters.
# The result is that file names which contain meta characters, FAILS.
# So it interprets '\A' as 'A' and whitespace as a delimiter!
grep: /tmp/file: No such file or directory
grep: A: No such file or directory
grep: /tmp/file: No such file or directory
grep: B: No such file or directory
grep: /tmp/file: No such file or directory
grep: C: No such file or directory
grep: /tmp/file: No such file or directory
grep: $D: No such file or directory
=====
ERROR: All files in the sample list FAIL!
=====

# Use xargs -I{} to avoid problems of whitespace in filenames
# But the args are further interpreted by bash, as in escape '\' expansion.
# Bash still interprets xarg's '\A' as 'A' and so 'grep' processes the wrong file
# However the -I{} does protect the D from var expansion
/tmp/file   A:text-A
/tmp/file   C:text-C
/tmp/file   $D:quirk 2. $D in filename
=====
ERROR: The 1st line refers to 'file   A' which is NOT in the list!
=====

# Use xargs -0 to avoid problems of whitespace in filenames
# 'xargs -0' goes further with parameter protection than -I.
# Quotes and backslash are not special (every character is taken literally)
/tmp/file   \A:quirk 1. \A in filename
/tmp/file   C:text-C
/tmp/file   $D:quirk 2. $D in filename
==
OK
==

=====================================
Passing parameters directly to 'grep'
=====================================

# Use 'grep' with the assumption that every file name contains no meta characters.
# The result is that file names which contain meta characters, FAILS.
grep: /tmp/file: No such file or directory
grep: \A: No such file or directory
grep: /tmp/file: No such file or directory
grep: B: No such file or directory
grep: /tmp/file: No such file or directory
grep: C: No such file or directory
grep: /tmp/file: No such file or directory
grep: $D: No such file or directory
=====
ERROR: All files in the sample list FAIL!
=====

# Set bash positional parameters "$1" "$2" ... "$n"
# Note: destructive... original parameters are overwritten
#   and, you may need to reset $IFS to its original value
/tmp/file   \A:quirk 1. \A in filename
/tmp/file   C:text-C
/tmp/file   $D:quirk 2. $D in filename
==
OK
==

# Set bash positional parameters "$1" "$2" ... "$n"
# Note: non-destructive... original parameters are not overwritten
# Variable set in the sub-shell are NOT accessible on return.
# There is no need to reset $IFS
/tmp/file   \A:quirk 1. \A in filename
/tmp/file   C:text-C
/tmp/file   $D:quirk 2. $D in filename
==
OK
==

# Using bash array elements "${list[0]}" "${list[1]}" ... "${list[n-1]}"
# Note: you may need to reset $IFS to its original value
/tmp/file   \A:quirk 1. \A in filename
/tmp/file   C:text-C
/tmp/file   $D:quirk 2. $D in filename
==
OK
==