Open and write data to text file using Bash

Question

How can I write data to a text file automatically by shell scripting in Linux   I was able to open the file  However  I don t know how to write data to it

User · Answer

I like this answer   cat  gt  FILE txt  lt  lt EOF  info code info      EOF   but would suggest cat  gt  gt  FILE txt  lt  lt  EOF if you want just add something to the end of the file without wiping out what is already exists  Like this   cat  gt  gt  FILE txt  lt  lt EOF  info code info      EOF

User · Answer

Moving my comment as an answer  as requested by  lycono  If you need to do this with root privileges  do it this way    sudo sh -c  echo  some data for the file   gt  gt  fileName

User · Answer

The short answer  echo  quot some data for the file quot   gt  gt  fileName  However  echo doesn t deal with end of line characters  EOFs  in an ideal way  So  if you re gonna append more than one line  do it with printf  printf  quot some data for the file nAnd a new line quot   gt  gt  fileName  The  gt  gt  and  gt  operators are very useful for redirecting output of commands  they work with multiple other bash commands

User · Answer

this is my answer    cat file   copy file

User · Answer

bin bash  cat  gt  FILE txt  lt  lt EOF  info code info  info code info info code info  EOF

User · Answer

Can also use here document and vi  the below script generates a FILE txt with 3 lines and variable interpolation  VAR Test vi FILE txt  lt  lt EOFXX i  This is my var in text file var    VAR  Thats end of text file    ZZ EOFXX   Then file will have 3 lines as below   i  is to start vi insert mode and similarly to close the file with Esc and ZZ    This is my var in text file var   Test  Thats end of text file

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I know this is a damn old question  but as the OP is about scripting  and for the fact that google brought me here  opening file descriptors for reading and writing at the same time should also be mentioned      bin bash    Open file descriptor  fd  3 for read write on a text file  exec 3 lt  gt  poem txt        Let s print some text to fd 3     echo  Roses are red   gt  amp 3     echo  Violets are blue   gt  amp 3     echo  Poems are cute   gt  amp 3     echo  And so are you   gt  amp 3    Close fd 3 exec 3 gt  amp -   Then cat the file on terminal    cat poem txt Roses are red Violets are blue Poems are cute And so are you   This example causes file poem txt to be open for reading and writing on file descriptor 3  It also shows that  nix boxes know more fd s then just stdin  stdout and stderr  fd 0 1 2   It actually holds a lot  Usually the max number of file descriptors the kernel can allocate can be found in  proc sys file-max or  proc sys fs file-max but using any fd above 9 is dangerous as it could conflict with fd s used by the shell internally  So don t bother and only use fd s 0-9  If you need more the 9 file descriptors in a bash script you should use a different language anyways     Anyhow  fd s can be used in a lot of interesting ways

User · Answer

bin sh  FILE   path to file    bin cat  lt  lt EOM  gt  FILE text1 text2   This comment will be inside of the file  The keyword EOM can be any text  but it must start the line and be alone   EOM   This will be also inside of the file  see the space in front of EOM  EOM   No comments and spaces around here  or it will not work  text4  EOM

User · Answer

You can redirect the output of a command to a file     cat file  gt  copy file   or append to it    cat file  gt  gt  copy file   If you want to write directly the command is echo  text     echo  Hello World   gt  file

User · Answer

If you are using variables  you can use first var  quot Hello quot  second var  quot How are you quot   If you want to concat both string and write it to file  then use below echo  quot   first var  -   second var  quot   gt    file name txt  Your file name txt content will be  quot Hello - How are you quot

User · Answer

For environments where here documents are unavailable  Makefile  Dockerfile  etc  you can often use printf for a reasonably legible and efficient solution   printf   s n      bin sh     Second line           Third line           Conveniently mix single and double quotes  too           Generated   date              the date command executes when the file is generated         for file in    do             echo  Found  file          done   gt outputfile

User · Answer

I thought there were a few perfectly fine answers  but no concise summary of all possibilities  thus   The core principal behind most answers here is redirection  Two are important redirection operators for writing to files   Redirecting Output   echo  text to completely overwrite contents of myfile   gt  myfile  Appending Redirected Output  echo  text to add to end of myfile   gt  gt  myfile  Here Documents  Others mentioned  rather than from a fixed input source like echo  text   you could also interactively write to files via a  Here Document   which are also detailed in the link to the bash manual above  Those answers  e g    cat  gt  FILE txt  lt  lt EOF or cat  gt  gt  FILE txt  lt  lt EOF  make use of the same redirection operators  but add another layer via  Here Documents   In the above syntax  you write to the FILE txt via the output of cat  The writing only takes place after the interactive input is given some specific string  in this case  EOF   but this could be any string  e g    cat  gt  FILE txt  lt  lt  StopEverything  or cat  gt  gt  FILE txt  lt  lt  StopEverything   would work just as well  Here Documents also look for various delimiters and other interesting parsing characters  so have a look at the docs for further info on that   Here Strings  A bit convoluted  and more of an exercise in understanding both redirection and Here Documents syntax  but you could combine Here Document style syntax with standard redirect operators to become a Here String   Redirecting Output of cat Input  cat  gt  myfile  lt  lt  lt  text to completely overwrite contents of myfile   Appending Redirected Output of cat Input  cat  gt  gt  myfile  lt  lt  lt  text to completely overwrite contents of myfile

[bash] Open and write data to text file using Bash?

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