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Is there any way to pipe the output of a command which lists a bunch of numbers (each number in a separate line) and initialize a bash array with those numbers?

Details: This lists 3 changelist numbers which have been submitted in the following date range. The output is then piped to cut to filter it further to get just the changelist numbers. 

p4 changes -m 3 -u edk -s submitted @2009/05/01,@now | cut -d ' ' -f 2

E.g. : 

422311
543210
444000

How is it possible to store this list in a bash array?

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3 Answers 3

Reset to default
73

You can execute the command under ticks and set the Array like,

ARRAY=(`command`)

Alternatively, you can save the output of the command to a file and cat it similarly,

command > file.txt
ARRAY=(`cat file.txt`)

Or, simply one of the following forms suggested in the comments below,

ARRAY=(`< file.txt`)
ARRAY=($(<file.txt))
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7 Comments

Useless use of cat: <file.txt does the same.
fixed the answer for future reference.
Whenever possible, avoid the use of back quotes. This is more readable and can work with nesting without awkward quoting: ARRAY=($(command)) or ARRAY=($(< file.txt))
Be warned that this will ALWAYS use whitespace to separate elements. stackoverflow.com/questions/9449417/… reports possibility to handle whitespace by setting IFS to '\n' but I couldn't make it accept '\0'.
Why does folders=(`ls -1 ${FOLDER} | xargs`) give me Syntax error: "(" unexpected ?
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16

If you use bash 4+, it has special command for this: mapfile also known as readarray, so you can fill your array like this:

declare -a a
readarray -t a < <(command)

for more portable version you can use

declare -a a
while read i; do
  a=( "${a[@]}" "$i" )
done < <(command)
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6 Comments

This is my first time seeing < <(command). Can you please help me find more detail on this syntax. I'm interested in knowing why it needs 2 < to work. Thanks
First < is redirection of input stream, see gnu.org/software/bash/manual/html_node/… for detains. Construction <(command) means that output of command is piped to named fifo (usually /dev/fdn), you can find details on it at gnu.org/software/bash/manual/html_node/….
Be warned that readarray doesn't support an alternative separator, it always uses newline.
a[${#a[*]}]=value or a+=(value) is a better syntax to append to an array.
Re @ivan_pozdeev readarray/mapfile apparently does support defining alternative delimiters. The docs specify -d delim: "The first character of delim is used to terminate each input line, rather than newline."
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3

Quite similar to #4 but looks a bit better for me. :)

declare -a a
readarray -t a <<< $(command)
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1 Comment

Interesting alternative. However the methods differ in case of an empty output from the command, the here-string method gives an array having one empty item, whereas the names pipe method gives an empty array.

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