View source for Bourne Shell Scripting/Appendix C: Quick Reference

This final section provides a fast lookup reference for the materials in this document.  It is a collection of thumbnail examples and rules that will be cryptic if you haven't read through the text.

== Useful commands ==

{| class="wikitable" width="100%" border="1" cellspacing="0" cellpadding="5"
! | Command
! | Effect
|-
| cat
| Lists a file or files sequentially.
|-
| cd                   
| Change directories.
|-
| chmod ugo+rwx        
| Set read, write and execute permissions for user, group and others.
|-
| chmod a-rwx          
| Remove read, write and execute permissions from all.
|-
| chmod 755            
| Set user write and universal read-execute permissions
|-
| chmod 644            
| set user write and universal read permissions.
|-
| cp                   
| Copy files.
|-
| expr 2 + 2           
| Add 2 + 2.
|-
| fgrep                
| Search for string match.
|-
| grep                 
| Search for string pattern matches.
|-
| grep -v              
| Search for no match.
|-
| grep -n              
| List line numbers of matches.
|-
| grep -i              
| Ignore case.
|-
| grep -l              
| Only list file names for a match.
|-
| head -n5 source.txt   
| List first 5 lines.
|-
| less
| View a text file one screen at a time; can scroll both ways.
|-
| ll                   
| Give a listing of files with file details.
|-
| ls                   
| Give a simple listing of files.
|-
| mkdir                
| Make a directory.
|-
| more                 
| Displays a file a screenfull at a time.
|-
| mv                   
| Move or rename files.
|-
| paste f1 f2          
| Paste files by columns.
|-
| pg                   
| Variant on "more".
|-
| pwd                  
| Print working directory.
|-
| rm                   
| Remove files.  
|-
| rm -r                
| Remove entire directory subtree.
|-
| rmdir                
| Remove an empty directory.
|-
| sed 's/txt/TXT/g'    
| Scan and replace text.
|-
| sed 's/txt/d'        
| Scan and delete text.
|-
| sed '/txt/q'         
| Scan and then quit.
|-
| sort                 
| Sort input.
|-
| sort +1              
| Skip first field in sorting. 
|-
| sort -n              
| Sort numbers. 
|-
| sort -r              
| Sort in reverse order.
|-
| sort -u              
| Eliminate redundant lines in output.
|-
| tail -5 source.txt   
| List last 5 lines.
|-
| tail +5 source.txt   
| List all lines after line 5.
|-
| tr '[A-Z]' '[a-z]'   
| Translate to lowercase.
|-
| tr '[a-z]' '[A-Z]'   
| Translate to uppercase.
|-
| tr -d '_'            
| Delete underscores.
|-
| uniq                 
| Find unique lines. 
|-
| wc                   
| Word count (characters, words, lines).
|-
| wc -w                
| Word count only.
|-
| wc -l                
| Line count.
|}

== Elementary shell capabilities ==

{| class="wikitable" width="100%" border="1" cellspacing="0" cellpadding="5"
! | Command
! | Effect
|-
| shvar="Test 1"       
| Initialize a shell variable.
|-
| echo $shvar          
| Display a shell variable.
|-
| export shvar         
| Allow subshells to use shell variable.
|-
| mv $f ${f}2 ''or'' mv ${f}{,2}
| Append "2" to file name in shell variable.
|-
| $1, $2, $3, ...      
| Command-line arguments.
|-
| $0                   
| Shell-program name.
|-
| $#                   
| Number of arguments.
|-
| $*                   
| Complete argument list (all in one string).
|-
| $@                   
| Complete argument list (string for every argument).
|-
| $?              
| Exit status of the last command executed.
|-
| shift 2              
| Shift argument variables by 2.
|-
| read v               
| Read input into variable "v".
|-
| . mycmds             
| Execute commands in file.
|}

== IF statement ==

The if statement executes the command between <code>if</code> and <code>then</code>. If the command returns not 0 then the commands between <code>then</code> and <code>else</code> are executed - otherwise the command between <code>else</code> and <code>fi</code>.
<syntaxhighlight lang="shell">

   if test "${1}" = "red" ; then
     echo "Illegal code."
   elif test "${1}" = "blue" ; then
     echo "Illegal code."
   else
     echo "Access granted."
   fi

   if [ "$1" = "red" ]
   then
     echo "Illegal code."
   elif [ "$1" = "blue" ]
   then
     echo "Illegal code."
   else
     echo "Access granted."
   fi 
</syntaxhighlight>
==== Test Syntax Variations ====

Most test commands can be written using more than one syntax. Mastering and consistently using one form may be a programming best-practice, and may be a more efficient use of overall time.

==== String Tests ====

String Tests are performed by the <code>test</code> command. See <code>help test</code> for more details. To make scripts look more like other programming languages the synonym <code>[ ... ]</code> was defined which does exactly the same as <code>test</code>.

{| class="wikitable" width="100%" border="1" cellspacing="0" cellpadding="5"
! | Command
! | Effect
|-
| test "$shvar" = "red"<br>
[ "$shvar" = "red" ]
| String comparison, true if match.
|-
|test "$shvar" != "red"<br>
[ "$shvar" != "red" ] 
| String comparison, true if no match.
|-
|test -z "${shvar}"<br>
test  "$shvar" = ""<br>
[ "$shvar" = "" ]
|        True if null variable.
|-
|test -n "${shvar}"<br>
test  "$shvar" != ""<br>
[ -n "$shvar" ]<br>
[ "$shvar" != "" ]
|       True if not null variable.
|}

==== Arithmetic tests ====

simple arithmetics can be performed with the <code>test</code> for more complex arithmetics the <code>let</code> command exists. See <code>help let</code> for more details. Note that for <code>let</code> command variables don't need to be prefixed with '$' and the statement need to be one argument, use <code>'...'</code> when there are spaces inside the argument. Like with <code>test</code> a synonym - <code>(( ... ))</code> - was defined to make shell scripts look more like ordinary programs.

{| class="wikitable" width="100%" border="1" cellspacing="0" cellpadding="5"
! | Command
! | Effect
|-
|test  "$nval" -eq 0<br>
let 'nval == 0'<br>
[ "$nval" -eq 0 ]<br>
(( nval == 0 ))
|        Integer test; true if equal to 0.
|-
|test  "$nval" -ge 0<br>
let 'nval >= 0'<br>
[ "$nval" -ge 0 ]<br>
(( nval >= 0 ))
|        Integer test; true if greater than or equal to 0.
|-
|test  "$nval" -gt 0<br>
let 'nval > 0'<br>
[ "$nval" -gt 0 ]<br>
(( nval > 0 ))
|        Integer test; true if greater than 0.
|-
|test  "$nval" -le 0<br>
let 'nval <= 0'<br>
[ "$nval" -le 0 ]<br>
(( nval <= 0 ))
|        Integer test; true if less than or equal to 0.
|-
|test  "$nval" -lt 0<br>
let 'nval < 0'<br>
[ "$nval" -lt 0 ]<br>
(( nval < 0 ))
|        Integer test; true if less than to 0.
|-
|test  "$nval" -ne 0<br>
let 'nval != 0'<br>
[ "$nval" -ne 0 ]<br>
(( nval != 0 ))
|        Integer test; true if not equal to 0.
|-
|let 'y + y > 100'<br>
(( y + y >= 100))
|        Integer test; true when <math>x + y \ge 0</math>
|}

==== File tests ====

{| class="wikitable" width="100%" border="1" cellspacing="0" cellpadding="5"
! | Command
! | Effect
|-
|test  -d tmp<br>
[ -d tmp ]
|               True if "tmp" is a directory.
|-
|test  -f tmp<br>
[ -f tmp ]
|               True if "tmp" is an ordinary file.
|-
|test  -r tmp<br>
[ -r tmp ]
|               True if "tmp" can be read.
|-
|test  -s tmp<br>
[ -s tmp ]
|               True if "tmp" is nonzero length.
|-
|test  -w tmp<br>
[ -w tmp ]
|               True if "tmp" can be written.
|-
|test  -x tmp<br>
[ -x tmp ]
|               True if "tmp" is executable.
|}

==== Boolean tests ====

Boolean arithmetic is performed by a set of operators. It is important to note then the operators execute programs and compare the result codes. Because boolean operators are often combined with <code>test</code> command a unifications was created in the form of <code><nowiki>[[ ... ]]</nowiki></code>.

{| class="wikitable" width="100%" border="1" cellspacing="0" cellpadding="5"
! | Command
! | Effect
|-
|test  -d /tmp && test -r /tmp<br>
<nowiki>[[ -d /tmp && -r /tmp ]]</nowiki>
| True if "/tmp" is a directory and can be read.
|-
|test  -r /tmp <nowiki>||</nowiki> test -w /tmp
<nowiki>[[ -r /tmp || -w /tmp ]]</nowiki>
| True if "tmp" can be read or written.
|-
|test ! -x /tmp<br>
<nowiki>[[ ! -x /tmp ]]</nowiki>
| True if the file is not executable
|}

== CASE statement ==
<syntaxhighlight lang="shell">

   case "$1" 
   in
     "red")      echo "Illegal code."
                 exit;;
     "blue")     echo "Illegal code."
                 exit;;
     "x"|"y")    echo "Illegal code."
                 exit;;
     *)          echo "Access granted.";;
   esac

</syntaxhighlight>
== Loop statements ==
<syntaxhighlight lang="shell">
   for nvar in 1 2 3 4 5
   do
     echo $nvar
   done 

   for file            # Cycle through command-line arguments.
   do
     echo $file
   done

   while [ "$n" != "Joe" ]     # Or:   until [ "$n" == "Joe" ]
   do
     echo "What's your name?"
     read n
     echo $n
   done
</syntaxhighlight>
There are "break" and "continue" commands that allow you to exit or skip to
the end of loops as the need arises.

Instead of [] we can use test.
[] requires space after and before the brackets and there should be spaces between arguments.

== Credit ==

This content was originally from http://www.vectorsite.net/tsshell.html and was originally in the public domain.

<noinclude>
{{auto navigation|Appendix D: Cookbook|Appendix B: Environment reference}}
{{BookCat}}
</noinclude>