Unix Shell Script

0 stdin
1 stdout
2 stderr

# Redirect stdout to a file:
1>filename
echo "test" 1>stdout.txt
 
# Redirect stdout and append to a file:
1>>filename
 
# Redirect stderr to a file:
2>filename
 
# Redirect stderr and append to a file:
2>>filename
 
# Redirect both stdout and stderr to a file:
&>filename
 
# Send stderr to stdout
2>&1	
 
# Redirect file descriptor i to j
i>&j
 
# Redirect i to j
>&j = 1>&j	
 
# Close stdin
<&-
 
# Close stdout
>&-
 
# Read stdin from file
0<filename
<filename	grep "test" < test.txt

for i in 'ls | grep jar'
do
	echo "$i"
done

i=1
while [ "$i" -le 5 ]
do
	echo "$i"
	i='expr $i + 1'
done

if [ ]
then
  # do something
elif [ ]
then
  # do something
else
  # do something
fi

* If cmd1 succeeds go to cmd2
cmd1 && cmd2

* If cmd1 fails then go to cmd2
cmd1 || cmd2

-b FILE # FILE exists and is block special
-c FILE # FILE exists and is character special
-d FILE # FILE exists and is a directory
-e FILE # FILE exists
-f FILE # FILE exists and is a regular file
-g FILE # FILE exists and is set-group-ID
-G FILE # FILE exists and is owned by the effective group ID
-h FILE # FILE exists and is a symbolic link (same as -L)
-k FILE # FILE exists and has its sticky bit set
-L FILE # FILE exists and is a symbolic link (same as -h)
-O FILE # FILE exists and is owned by the effective user ID
-p FILE # FILE exists and is a named pipe
-r FILE # FILE exists and read permission is granted
-s FILE # FILE exists and has a size greater than zero
-S FILE # FILE exists and is a socket
-t FD # File descriptor FD is opened on a terminal
-u FILE # FILE exists and its set-user-ID bit is set
-w FILE # FILE exists and write permission is granted
-x FILE # FILE exists and execute (or search) permission is granted

-eq
-ne
-gt
-ge
-lt
-le

[ s1 = s2 ]  # s1 equals to s2
[ s1 == s2 ] # synonym for =
[ s1 != s2 ] # s1 not equal to s2
[ s ]        # is not null
[ -n s ]     # s is not null
[ -z s ]     # s is null

! not
-a and
-o or

* Begins with an alphabetic or underscore character
* Followed by zero or more alphanumeric or underscore characters
* No spaces

* No data type concept
* No need to declare

* var=val # Notice no spaces before or after equal sign

* $var
* ${var}

* Use eval derefVar=\$$var to do de-referencing.
* After de-referencing, derefVar will contain value referenced by $var.

#!/usr/bin/sh
var1=VariableOne
echo "\$var1=$var1"
 
var2=var1
echo
echo "Before dereferencing..."
echo "\$var2=$var2"
 
echo
echo "After dereferencing..."
eval derefVar2=\$$var2
echo "\$derefVar2=$derefVar2"
 
# Result:
$var1=VariableOne
 
Before dereferencing...
$var2=var1
 
After dereferencing...
$derefVar2=VariableOne

* Operators: + – * / %
* Need spaces around input numbers.
* Need to escape * character.
* Examples:

expr 1 + 2
3

# If no spaces around input numbers:
expr 1+2
1+2

# Need to escape *
$ expr 2 \* 2
4

# Otherwise
$ expr 2 * 2
expr: syntax error

# Assign result
$ i=1
$ i=`expr $i + 1`    # Notice the back quotes
$ echo $i
2

$0: name of calling prog
$1 $2…: each individual argument
$*: all arguments
$@: a list of separate arguments
$$: pid of the process being exceed # Good for temp file name
$?: exit status
$#: count of args

IFS=”:” Internal field separater
HOME
MAIL
MAILCHECK
PS1
PS2
SHELL

\010  Backspace
\011  Tab
\012  New line character
\013  Line feed
\014  Form feed
\015  CR character
\033  Escape

* As an escape character:

$ echo \\
\
$ echo \$x
$x

* For continuing lines when used as last character on the line:

$ lines=one'     # Single quotes tell shell to ignore newline
> 'two
$ echo $lines
one two

$ lines=one\
> two
$ echo $lines
onetwo

* Ignore all quoted characters, for example:

$ echo '<> | / \ ` $'
<> | / \ ` $

* ignore most enclosed characters except $, \ (backslash), ` (back quotes).
* Examples:

$ name=jim

$ echo "name: ${name}"
name: jim

$ echo "name: \${name}"
name: ${name}

$ echo `date`
Thu May 28 12:34:58 EDT 2009

* Execute command:

$ echo `date`
Thu May 28 12:34:58 EDT 2009

* Result reformatted into one line

* Example

#!/usr/bin/bash
 
fxn1 () {
  if [ $# -ne 1 ]; then
    echo "Please provide one argument."
    exit 1
  else
    echo "Got argument via \$1: $1"
  fi
 
  if [ $1 = "ok" ]; then
    echo "Got ok"
    return 0
  else
    echo "Not ok"
    return 1
  fi
}
 
echo
echo "Calling fxn1 with argument..."
fxn1 ok
echo "\$?: $?"
echo
echo "Calling fxn1 with argument..."
fxn1 notok
echo "\$?: $?"
echo
echo "Calling fxn1 without argument..."
fxn1

* Result

 
Calling fxn1 with argument...
Got argument via $1: ok
Got ok
$?: 0
 
Calling fxn1 with argument...
Got argument via $1: notok
Not ok
$?: 1
 
Calling fxn1 without argument...
Please provide one argument.

#!/bin/sh
echo "delete...?"
read ok
if [ "$ok" = "y" ]; then
	echo "file name?"
	read file_to_del
	echo "deleting..."
	rm $file_to_del
	echo "done."
else
	echo "none deleted"
	exit 1
fi

* basename /this/is/a/dir/file gives file
* dirname /this/is/a/dir/file gives /this/is/a/dir

trap “” 15
0 Exit from shell
1 Hangup
2 Interrupt
15 Software termination signal

* used for column cutting.

cut -cchars file
where chars specifies what characters to extract 
from each line of file.
 
command                    extracts
who | cut -c5              character 5
who | cut -c1,13,50        characters 1, 13 and 50
who | cut -c20-50          characters 20 throught 50
who | cut -c5-             characters 5 to the end of line 
 
cut

* Translate or replace characters
* Example, replace underscore with space character:

str="str1_str2"; echo $str|tr '_' ' '
str1 str2

${smso}text${rmso}

Notation    Meaning                  Example        Matches
.           any character            a..            a followed by any two characters

^           beginning of line        ^hello         hello only if it appears at the beginning of the line

$           end of line              friend$        friend only if it appears at the end of the line

*           zero or more             x*             zero or more x's
            occurrence of            xx*            one or more x's
            previous reg exp         .*             zero or more characters

[chars]     any char in chars        [tT]           lower or upper case t
                                     [a-z]          lower case letter
                                     [a-zA-Z]       lower or upper case letter

[^chars]    any char                 [^0-9]         any non-numeric char 
            NOT in chars             [^a-zA-Z]      any non-alphabetic char

\{min,max\} at least min and         x\{1,5\}       at least 1, at most 5 x's
            at most max occurrences  [0-9]\{3,9\}   3 to 9 consecutive digits
            of previous reg exps     [0-9]\{3\}     exactly 3 digits
                                     [0-9]\{3,\}    at least 3 digits

\(...\)     store char matched       ^\(.\)         first char in line and stores it in register 1
            between parentheses      ^\(.\)\1       first two characters in line if they're the same
            in next register (1-9).                 
            retrieve register with
            \n. e.g. \1 retrieves
            values stored in first
            register

find \
[-P] \ # Never follow symbolic link. This is default.
[-L] \ # Follow symbolic link.
[-H] \ # Do not follow symbolic link except when processing command line arguments.
[path…] \

-daystart \ # Measure times from the beginning of the day instead of default 24 hrs ago.
-depth \ # Process directory contents first
-d \ # same as -depth
-help \
-maxdepth \ # Descent at most levels. -maxdepth 0 mean current dir
-mindepth \ # Start find only at designated levels. -mindepth 1 excludes command line dir.
-mount \ # Do not descent directories in other file systems
-noleaf \ # Do not assume Unix filesystem to accommodate CDROM etc
-regextype type \ # Default to emac
-version \
-warn, -nowarn \ # Turn warning on and off
-xdev \ # Same as -mount

# +n: greater than, -n: less than, n: exactly n
-amin n \ # File last accessed n minutes ago
-anewer file \
-atime n \ # Access n*24 hours ago
-cmin n \ # Last changed n minutes ago
-cnewer file \
-ctime n \
-empty \ # File is empty
-fstype type \
-gid n \ # File numeric group id is n
-group gname \ # File belongs to gname group name
-ilname \ # Like -lname but case insensitive
-iname \ # Like -name but case insensitive
-iregex \ # Like -regex but case insensitive
-links n \ # File has n links
-lname pattern \ # Symbolic links matching pattern
-mmin n \ # Last modified n minutes ago
-mtime n \ # Last modified n*24 minutes ago
-name pattern \
-newer file \ # Last modified newer than file
-nouser \
-nogroup \
-path pattern \
-perm mode \
-perm -mode \
-regex pattern \
-samefile name \
-size n[cwbkMG] \
-type [bcdpflsD] \ # Type of byte, char, dir, pipe, file, link,socket,door (Solaris)
-uid n \ # Owned by uid of n
-used n \
-user uname \ # Owned by uname
-wholename pattern \ # Matches shell pattern of pattern
-xtype

find ./ FTP.LOG -exec rm {} \;
 
find / -size +1000000000c;
(look for files larger than 1gb)
 
# Find jpg files
find . -type f -name "*.jpg" -print
 
# Find files larger than 10KB and list their details
find . -type f -size +10000 -exec ls -al {} \;
 
# Find files accessed two days ago and list their details
find . -atime +2 -type f -exec ls -al {} \;
 
# Find files modified 90 days ago and list their details
find . -mtime +90 -type f -exec ls -al {} \;
 
# Find files modified about 10 minutes ago and list their details
  # Find current date time
  >date
  Tuesday, July 13, 2010 02:22:59 PM GMT
 
  # Create an empty anchor file with time stamp set to 10 min ago
  >touch -t 201007131412 /tmp/mytemptime.tmp 
 
  >ls -l /tmp/mytemptime.tmp
  -rw-r--r--   1 oracle   dba  0 Jul 13 14:12 /tmp/mytemptime.tmp
 
  # Find all files newer than the anchor file
  >find . -type f -newer /tmp/mytemptime.tmp -exec ls -l {} \;
  -rw-r-----   1 oracle   dba  97013 Jul 13 14:25 ./Apache/Apache/logs/access_log.1279022400
 
# Find "admin" string in all properties files
find . -type f -name "*.properties" -exec grep -i "admin" {} \; 
 
# Find "admin" string in all properties files, also list file name
find . -type f -name "*.properties" -print -exec grep -i "admin" {} \; 
 
# Find all *non* zip files
find . -type f \! -name "*.zip" -print
 
# Find *non* zip and *non* txt files
find . -type f \! -name "*.zip" \! -name "*.txt" -print
 
# Find files owned by jboss
find -user jboss
 
# Find files accessed two days ago from today's day start time i.e. 0:00am
find . -atime +2 -daystart
 
# Find properties files in the next two levels of subdirectories.
find . -name "*.properties" -depth -print -maxdepth 2
 
# Find empty files
find . -empty -type f

* More Bash Examples