How to read a file into a variable in shell

Question

I want to read a file and save it in variable  but I need to keep the variable and not just print out the file  How can I do this  I have written this script but it isn t quite what I needed      bin sh while read LINE   do     echo  LINE   done  lt  1   echo 11111-----------   echo  LINE     In my script  I can give the file name as a parameter  so  if the file contains  aaaa   for example  it would print out this   aaaa 11111-----   But this just prints out the file onto the screen  and I want to save it into a variable  Is there an easy way to do this

User · Accepted Answer

In cross-platform  lowest-common-denominator sh you use      bin sh value  cat config txt  echo   value    In bash or zsh  to read a whole file into a variable without invoking cat      bin bash value    lt config txt  echo   value    Invoking cat in bash or zsh to slurp a file would be considered a Useless Use of Cat   Note that it is not necessary to quote the command substitution to preserve newlines   See  Bash Hacker s Wiki - Command substitution - Specialities

User · Answer

Two important pitfalls  which were ignored by other answers so far    Trailing newline removal from command expansion NUL character removal   Trailing newline removal from command expansion  This is a problem for the   value    cat config txt     type solutions  but not for read based solutions   Command expansion removes trailing newlines   S    printf  a n    printf   S    od -tx1   Outputs   0000000 61 0000001   This breaks the naive method of reading from files   FILE    mktemp   printf  a n n   gt    FILE  S     lt   FILE    printf   S    od -tx1 rm   FILE    POSIX workaround  append an extra char to the command expansion and remove it later   S    cat  FILE  printf a   S    S a   printf   S    od -tx1   Outputs   0000000 61 0a 0a 0000003   Almost POSIX workaround  ASCII encode  See below   NUL character removal  There is no sane Bash way to store NUL characters in variables   This affects both expansion and read solutions  and I don t know any good workaround for it   Example   printf  a 0b    od -tx1 S    printf  a 0b    printf   S    od -tx1   Outputs   0000000 61 00 62 0000003  0000000 61 62 0000002   Ha  our NUL is gone   Workarounds    ASCII encode  See below  use bash extension     literals   S   a 0b  printf   S    od -tx1   Only works for literals  so not useful for reading from files    Workaround for the pitfalls  Store an uuencode base64 encoded version of the file in the variable  and decode before every usage   FILE    mktemp   printf  a 0 n   gt    FILE  S    uuencode -m   FILE   dev stdout   uudecode -o  dev stdout  lt  printf   S     od -tx1 rm   FILE    Output   0000000 61 00 0a 0000003   uuencode and udecode are POSIX 7 but not in Ubuntu 12 04 by default  sharutils package     I don t see a POSIX 7 alternative for the bash process  lt    substitution extension except writing to another file     Of course  this is slow and inconvenient  so I guess the real answer is  don t use Bash if the input file may contain NUL characters

User · Answer

With bash you may use read like tis     usr bin env bash    IFS  read -rd    value  lt config txt   2 gt  dev null  printf   s   quot  value quot   Notice that   The last newline is preserved   The stderr is silenced to  dev null by redirecting the whole commands block  but the return status of the read command is preserved  if one needed to handle read error conditions

User · Answer

If you want to read the whole file into a variable      bin bash value  cat sources xml  echo  value   If you want to read it line-by-line   while read line  do         echo  line     done  lt  file txt

User · Answer

As Ciro Santilli notes using command substitutions will drop trailing newlines  Their workaround adding trailing characters is great  but after using it for quite some time I decided I needed a solution that didn t use command substitution at all  My approach now uses read along with the printf builtin s -v flag in order to read the contents of stdin directly into a variable    Reads stdin into a variable  accounting for trailing newlines  Avoids   needing a subshell or command substitution    Note that NUL bytes are still unsupported  as Bash variables don t allow NULs    See https   stackoverflow com a 22607352 113632 read input         Use unusual variable names to avoid colliding with a variable name     the user might pass in  notably  quot contents quot        quot   1  Must provide a variable to read into  quot    if     quot  1 quot       line      quot  1 quot       contents      then     echo  quot Cannot store contents to  1  use a different name  quot   gt  amp 2     return 1   fi    local  line  contents       while IFS    read -r  line  do       contents    quot   line quot    n      done      include   line once more to capture any content after the last newline    printf -v  quot  1 quot    s   quot    contents     quot   quot   line quot     This supports inputs with or without trailing newlines  Example usage    read input file contents  lt   tmp file    file contents now contains the contents of  tmp file

User · Answer

this works for me   v   cat  lt file path gt   echo  v

User · Answer

You can access 1 line at a time by for loop     bin bash -eu   This script prints contents of  etc passwd line by line  FILENAME   etc passwd  I 0 for LN in   cat  FILENAME  do     echo  Line number    I     -- gt    LN  done   Copy the entire content to File  say line sh     Execute   chmod  x line sh   line sh

[shell] How to read a file into a variable in shell?

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