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I have this bash script:

for opt in string1 string2 string3 ... string99
do somestuff

It works, but I would like to replace the explicit listing of my strings with a file which actually contains all the strings; something like this:

strings=loadFromFile
for opt in $strings
do somestuff

How should I do this?

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5 Answers 5

up vote 6 down vote accepted

while read VAR is probably best here, as it handles per-line input. You can redirect it from a file, e.g.:

while IFS= read -r THELINE; do
  echo "..$THELINE"
done </path/to/file

That'll give you each line prepended with ".."

For your example case:

while IFS= read -r opt; do
  #somestuff $opt
done </path/to/file

See Why is `while IFS= read` used so often, instead of `IFS=; while read..`? for explanations.

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3  
Putting cats into pipes is bad behavior from a memory management point of view. especially when using "filter" built-in commands. @rush's answer is better, and what I use on a daily basis. –  David Kohen Sep 19 '12 at 14:15
3  
It also puts the while loop into a subshell, which can cause confusing behaviour if update variable values in the loop (the values will disappear when the subshell exits) –  glenn jackman Sep 19 '12 at 15:48
    
If somestuff includes another read, this seems not to work properly. –  Raphael Feb 23 '13 at 19:04
    
@raphael - in what way does it not "work properly"? I just tried nested reads and it works fine. –  IBBoard Feb 24 '13 at 13:52
    
@IBBoard See this new question. –  Raphael Feb 24 '13 at 15:59

My advice:

cat INPUTFILE| {
  declare -a LINES
  mapfile -t LINES
  for line in "${LINES[@]}"
  do
    somestuff
  done
}
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Syntax error: bad substitution –  michelemarcon Sep 19 '12 at 13:34
1  
Works for me. @michelemarcon, is your bash 4.00 or never? –  manatwork Sep 19 '12 at 13:36
    
GNU bash, version 2.05a.0(1)-release (arm-unknown-linux-gnu) –  michelemarcon Sep 19 '12 at 13:42
4  
That is ancient. Please specify this requirement in the question. –  manatwork Sep 19 '12 at 13:46
while IFS= read -r opt
do 
    some_stuff
done < file_with_string

See Why is `while IFS= read` used so often, instead of `IFS=; while read..`? for explanations.

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Why don't you use the readarray builtin (requires bash >= 4.0)?

readarray < FileNameFromWhereToLoad    # push every line of 
                                       # 'FileNameFromWhereToLoad' onto 
                                       # $MAPFILE by default

for i in $MAPFILE ; do
    echo $i
done
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This also requires newer version of bash. –  David Kohen Sep 19 '12 at 14:12
    
i wouldn't call bash >= 4 new (release date was February 2009)! –  user1146332 Sep 19 '12 at 14:31
1  
Since he's using 2.05a, it is newer than what the asker has. In addition, some companies have avoided GPLv3 versions of bash, so do not have it in their system. –  David Kohen Sep 19 '12 at 14:36
    
Do you have a crystal ball around? But yes, i agree with you about your last statement, i will add the version requirement of readarray to my answer. –  user1146332 Sep 19 '12 at 14:39
1  
I didn't read that. Thanks for the hint ;) Maybe my answer is of value for somebody who will search for an answer for a similar question!? –  user1146332 Sep 19 '12 at 14:56

The while IFS= read -r line; do ...; done < aFile is the best answer

If your strings do not contain whitespace or \[*?, you could do

for word in $(< aFile); do something; done

$(< file) is a bash feature that reads the file (like cat except without having to spawn a new process).

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