Shell - Write variable contents to a file

Question

I would like to copy the contents of a variable  here called var  into a file   The name of the file is stored in another variable destfile    I m having problems doing this  Here s what I ve tried   cp  var  destfile   I ve also tried the same thing with the dd command    Obviously the shell thought that  var was referring to a directory and so told me that the directory could not be found    How do I get around this

User · Answer

If I understood you right  you want to copy  var in a file  if it s a string    echo  var  gt   destdir

User · Answer

Use the echo command   var  text to append   destdir  some directory path filename  if   -f   destdir    then      echo   var   gt    destdir  fi   The if tests that  destdir represents a file   The  gt  appends the text after truncating the file  If you only want to append the text in  var to the file existing contents  then use  gt  gt  instead   echo   var   gt  gt    destdir    The cp command is used for copying files  to files   not for writing text to a file

User · Answer

All of the above work  but also have to work around a problem  escapes and special characters  that doesn t need to occur in the first place  Special characters when the variable is expanded by the shell  Just don t do that  variable expansion  in the first place  Use the variable directly  without expansion  Also  if your variable contains a secret and you want to copy that secret into a file  you might want to not have expansion in the command line as tracing command echo of the shell commands might reveal the secret  Means  all answers which use  var in the command line may have a potential security risk by exposing the variable contents to tracing and logging of the shell  Use this  printenv var  gt file  That means  in case of the OP question  printenv var  gt  quot  destfile quot   Note  variable names are case sensitive

User · Answer

echo has the problem that if var contains something like -e  it will be interpreted as a flag  Another option is printf  but printf   var   gt    destdir  will expand any escaped characters in the variable  so if the variable contains backslashes the file contents won t match  However  because printf only interprets backslashes as escapes in the format string  you can use the  s format specifier to store the exact variable contents to the destination file   printf   s    var   gt    destdir

User · Answer

When you say  copy the contents of a variable   does that variable contain a file name  or does it contain a name of a file   I m assuming by your question that  var contains the contents you want to copy into the file     echo   var   gt    destdir    This will echo the value of  var into a file called  destdir  Note the quotes  Very important to have   var  enclosed in quotes  Also for   destdir  if there s a space in the name  To append it     echo   var   gt  gt    destdir

User · Answer

None of the answers above work if your variable    starts with -e starts with -n starts with -E contains a   followed by an n should not have an extra newline appended after it   and so they cannot be relied upon for arbitrary string contents   In bash  you can use  here strings  as   cat  lt  lt  lt    var   gt    destdir      As noted in the comment below   Trebawa s answer  formulated in the same room as mine   using printf is a better approach

[linux] Shell - Write variable contents to a file

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