Using variables inside a bash heredoc

Question

I m trying to interpolate variables inside of a bash heredoc   var  1 sudo tee   path to outfile   gt   dev null  lt  lt   EOF  Some text that contains my  var EOF   This isn t working as I d expect   var is treated literally  not expanded    I need to use sudo tee because creating the file requires sudo   Doing something like   sudo cat  gt   path to outfile  lt  lt EOT my text    EOT   Doesn t work  because  gt outfile opens the file in the current shell  which is not using sudo

User · Accepted Answer

In answer to your first question  there s no parameter substitution because you ve put the delimiter in quotes - the bash manual says      The format of here-documents is          lt  lt  - word               here-document       delimiter       No  parameter expansion  command substitution  arithmetic expansion  or   pathname expansion is performed on word   If any characters in word are   quoted   the  delimiter is the result of quote removal on word  and the   lines in the here-document are not expanded   If word is unquoted   all   lines  of  the here-document are subjected to parameter expansion  command substitution  and arithmetic expansion          If you change your first example to use  lt  lt EOF instead of  lt  lt   EOF  you ll find that it works   In your second example  the shell invokes sudo only with the parameter cat  and the redirection applies to the output of sudo cat as the original user   It ll work if you try   sudo sh -c  cat  gt   path to outfile   lt  lt EOT my text    EOT

User · Answer

As a late corolloary to the earlier answers here  you probably end up in situations where you want some but not all variables to be interpolated   You can solve that by using backslashes to escape dollar signs and backticks  or you can put the static text in a variable   Name  Rich Ba tard  dough     dollars     cat  lt  lt     HERE  Name  you can win a lot of  dough this week  Notice that   backticks  need escaping if you want literal text  not  pwd   just like in variables like   HOME  current value   HOME      HERE   Demo  https   ideone com rMF2XA  Note that any of the quoting mechanisms --      HERE or      HERE  or      HERE  -- will disable all variable interpolation  and turn the here-document into a piece of literal text   A common task is to combine local variables with script which should be evaluated by a different shell  programming language  or remote host   local   uname  ssh -t remote  lt  lt       echo   local is the value from the host which ran the ssh command        Prevent here doc from expanding locally  remote won t see backslash     remote    uname        Same here     echo    remote is the value from the host we ssh ed to

User · Answer

Don t use quotes with  lt  lt EOF   var  1 sudo tee   path to outfile   gt   dev null  lt  lt EOF Some text that contains my  var EOF   Variable expansion is the default behavior inside of here-docs  You disable that behavior by quoting the label  with single or double quotes

[bash] Using variables inside a bash heredoc

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