Bash Shell Script Quick Reference

Snips of Scripts

This page will be most useful as quick references and are not of much value unless you are already familiar with shell scripting.

Quick Reference

exec -replaces the running process with a new one
exit n -quits the shell with exit status n
export -makes variables available to spawned shells

File Test Options

-b file	True if file exists and is a block special file
-c file	True if file exists and is a character special file
-d file	True if file exists and is a directory
-e file	True if file exists
-f file	True if file exists and is a regular file
-G file	True if file exists and is owned by the effective group ID
-g file	True if file exists and has SGID set
-k file	True if file exists and has its "sticky" bit set
-l file	True if file exists and is a symbolic link
-O file	True if file exists and is owned by effective ID
-p file	True if file exists and is a named pipe
-r file	True if file exists and is a readable
-S file	True if file exists and is a socket
-s file	True if file exists and has a size greater than zero
-u file	True if file exists and has SUID set
-w file	True if file exists and is writable
-x file	True if file exists and is executable
file1 -ef file2	True if both files have the same device and inode numbers
file1 -nt file2	True if file1 is newer (modification date) than file2
file1 -ot file2	True if file1 is older (modification date) than file2

String Test Options

string1 -a string2	True if both expressions are true
string1 -o string2	True if either expressions are true
-z string	True if the length of string is zero
-n string	True if the length of string is non-zero
string1 = string2	strings are equal
string1 != string2	strings not are equal

Integer Test Options

integer1 -eq integer2	True if integers are equal
integer1 -ge integer2	True if integer1 is greater than or equal to integer2
integer1 -gt integer2	True if integer1 is greater than integer2
integer1 -lt integer2	True if integer1 is less than integer2
integer1 -le integer2	True if integer1 is less than or equal to integer2
integer1 -ne integer2	True if integer1 is not equal to integer2

Array Options

declare -a ARRAY_1=( element1 element2 element3 ...elementN )	Create an Array in one line
echo ${#ARRAY_1[@]}	Print the number of elements in the array
echo ${ARRAY_1[@]}	Print all the elements in the array
echo ${ARRAY_1[3]}	Print one element in the array( example prints 4th element, first is 0)

Script Snipits

IF, WHILE, DO

if [ -z "$<variable>" ]; then
  while [ -z "$<variable>" ]
  do
  ....(some code)...
  done 
fi

FOR, DO, DONE

for i in  word1 word2 ...wordn
do
  action involving $i (which = word)
done

AWK & SED

NEW_VARIABLE="`/sbin/ifconfig -a|grep -A 2 eth0|awk '/inet/ { print $2 }'|sed -e s/addr://`"

MAIL Notification

# build the Message & Subject variables
   echo "No major canges in disk use on $HOSTNAME" > $MESSAGE
   echo "  " >> $MESSAGE
   echo "`cat $DISKUSE`" >> $MESSAGE
   echo "$HOSTNAME - Disk Space Report" > $SUBJECT

# send the message to address $EMAIL
echo "`cat $MESSAGE`" | mail -s "`cat $SUBJECT`" $EMAIL

Test if File Exists with Non-Zero Size
- ```
if [ -s $DIFFTEST ] ;then
    
```
Test for Exact Equal (of number value)
- ```
if [ $SCHEDULED == $ACTUAL ] ;then
    
```

Get IP Address

# get external address from by greping ifconfig 
EXIP="`ifconfig -a|grep -A 2 $EXIF|awk '/inet/ { print $2 }'\
   |sed -e s/addr://`"

Get Broadcast Address

EXBCAST="`ifconfig -a|grep -A 2 $EXIF|awk '/inet/ { print $3 }'\
  |sed -e s/Bcast://`"

Get DNS Server IP's

# get dns servers from resolv.conf file
# first line is path, next 3 are dns servers
NAMED1="`cat /etc/resolv.conf|grep -n nameserver|grep 2:\
 |sed -e s/nameserver//|sed -e s/2://`" 

NAMED2="`cat /etc/resolv.conf|grep -n nameserver|grep 3:\
 |sed -e s/nameserver//|sed -e s/3://`"

NAMED3="`cat /etc/resolv.conf|grep -n nameserver|grep 4:\
 |sed -e s/nameserver//|sed -e s/4://`"

Remove Spaces from Filenames

for x in `ls -1|sed -e s/"\ "/_/g`;do mv "`echo $x|sed -e s/_/"\ "/g`" ${x};done