One line if else condition in linux shell scripting

Question

I would like to have the equivelant of the following in a one line if else condition    maxline  cat journald conf   grep   SystemMaxUse    if    maxline      SystemMaxUse     then     sed  s   SystemMaxUse  SystemMaxUse 50M g  journald conf  gt  journald conf2     mv journald conf2 journald conf  else     echo  This file has been edited  You ll need to do it manually   fi     I m attempting to put this into a one line command  So far I ve gotten it all but the else portion of the command  Here s what I have so far     maxline  cat journald conf   grep   SystemMaxUse     amp  amp  if    maxline      SystemMaxUse      then sed  s   SystemMaxUse  SystemMaxUse 50M g  journald conf  gt  journald conf2  amp  amp  mv journald conf2 journald conf  fi   So how can I include the else portion of the above code into my command  Thank you for your help in advance

User · Answer

You can use like bellow     var0   var1 lt 98 9 21    the same as if    quot  var1 quot  -lt 98    then    var0 9 else    var0 21 fi  extends condition result-if-true result-if-false  I found the interested thing on the book  quot Advanced Bash-Scripting Guide quot

User · Answer

It looks as if you were on the right track  You just need to add the else statement after the     following the  then  statement  Also I would split the first line from the second line with a semicolon instead of joining it with   amp  amp     maxline  cat journald conf   grep   SystemMaxUse     if    maxline      SystemMaxUse      then sed  s   SystemMaxUse  SystemMaxUse 50M g  journald conf  gt  journald conf2  amp  amp  mv journald conf2 journald conf  else echo  This file has been edited  You ll need to do it manually    fi   Also in your original script  when declaring maxline you used back-ticks     instead of single quotes     which might cause problems

User · Answer

To summarize the other answers  for general use   Multi-line if   then statement  if   foo    then     a  b elif   bar    then     c  d else     e  f fi   Single-line version  if   foo    then a  amp  amp  b  elif   bar    c  amp  amp  d  else e  amp  amp  f  fi  Using the OR operator    foo  amp  amp  a  amp  amp  b        bar  amp  amp  c  amp  amp  d      e  amp  amp  f   Notes  Remember that the AND and OR operators evaluate whether or not the result code of the previous operation was equal to true success  0   So if a custom function returns something else  or nothing at all   you may run into problems with the AND OR shorthand  In such cases  you may want to replace something like   a  amp  amp  b   with     a     EXPECTEDRESULT     amp  amp  b    etc   Also note that   and   are technically commands  so whitespace is required around them   Instead of a group of  amp  amp  statements like then a  amp  amp  b  else  you could also run statements in a subshell like then    a  b    else  though this is less efficient  The same is true for doing something like result1    foo  a  b    result2    bar  c  d        result1  -o   result2    instead of   foo  amp  amp  a  amp  amp  b        bar  amp  amp  c  amp  amp  d    Though at that point you d be getting more into less-compact  multi-line stuff anyway

User · Answer

It s not a direct answer to the question but you could just use the OR-operator    grep   SystemMaxUse   journald conf  gt   dev null  amp  amp  sed -i  s   SystemMaxUse  SystemMaxUse 50M g  journald conf      echo  This file has been edited  You ll need to do it manually

[linux] One line if/else condition in linux shell scripting

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