Table of Contents

Looping: For

 

For Loop

for loop
Given below is the basic looping construct.
for argument in [list]
do 
 command(s)… 
done
During each pass through the loop, argument takes on the value of each successive variable in the list.
for arg in “$var1” “$var2” “$var3” … “$varN“

# In pass 1 of the loop, arg = $var1

# In pass 2 of the loop, arg = $var2

# In pass 3 of the loop, arg = $var3 #

…

# In pass N of the loop, arg = $varN

# Arguments in [list] quoted to prevent possible word splitting.
The argument list may contain wild cards.
If do is on the same line as for, there needs to be a semicolon after list.

for argument in [list] ; do 

 

 

 

Simple for loops:  Example

Simple for loops:  Example
Script
for planet in Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto

do

echo $planet  # Each planet on a separate line

done
Output
Mercury

Venus

Earth

Mars

Jupiter

Saturn

Uranus

Neptune

Pluto

 

for loops:  Example in Bash script
for loops:  Example in Bash script

 

 

Example
Script
for planet in “Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto”  

 

# All planets on same line.   

# Entire ‘list’ enclosed in quotes creates a single variable.   

# Why? Whitespace incorporated into the variable.

# Otherwise planet would be treated as a single variable

    do 

    echo $planet

    done
Output
Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto
Note: Each [list] element may contain multiple parameters. This is useful when processing

parameters in groups.
In such cases, use the set command to force the parsing of each [list] element and assignment of each component to the positional parameters.

 

 

 for loop with two parameters in each [list] element

 for loop with two parameters in each [list] element: Example
Script
for planet in “Mercury 36” “Venus 67” “Earth 93”  “Mars 142” “Jupiter 483“

    do 

set — $planet 

#  Parses variable “planet”  and sets positional parameters. 

#  The “–” prevents nasty surprises if $planet is null or begins with a dash. 

#  May need to save original positional parameters, since they get overwritten. 

#  One way of doing this is to use an array,

 # original_params=(“$@”) 

echo “$1  $2,000,000 miles from the sun” 

    done
Output
Mercury  36,000,000 miles from the sun

Venus  67,000,000 miles from the sun

Earth  93,000,000 miles from the sun

Mars  142,000,000 miles from the sun

Jupiter   483,000,000 miles from the sun

 

 for loop with two parameters in each [list] element: Example
for loop with two parameters in each [list] element: Example

 

Operating on a file list contained in a variable

Fileinfo.sh : operating on a file list contained in a variable: Example
Script
#!/bin/bash

#fileinfo.sh

FILES=”/usr/sbin/accept  /usr/sbin/pwck  /usr/sbin/chroot  /usr/bin/fakefile  /sbin/badblocks/  sbin/ypbind”    

# List of files you are curious about.                 

# Threw in a dummy file, /usr/bin/fakefile.

for file in $FILES

do 

         if [ ! -e “$file” ]      

# Check if file exists. 

         then    echo “$file does not exist.“     

fi 

ls -l $file  

 done

Output
lrwxrwxrwx 1 root root 10 Feb  5 14:30 /usr/sbin/accept -> cupsaccept

 –rwxr–xr-x. 1 root root 42416 Dec 7 2011 /usr/sbin/pwck

–rwxr–xr-x 1 root root 31776 Jan 23 2013 /usr/sbin/chroot

/usr/bin/fakefile does not exist.

–rwxr–xr-x 1 root root 29752 Jun 25 2012 /sbin/badblocks

/sbin/ypbind does not exist.

 

 

 

for loop example operating on a file list contained in a variable
for loop example operating on a file list contained in a variable

 

 

Operating on all files in the current directory using for loop

Operating on all files in the current directory using for loop
Script
for file in $PWD

# You cal also use ./  in place of $PWD

    do 

    ls -l “$file”  

# Lists all files in $PWD (current directory). 

Done
Generating the [list] in a for loop with command substitution
Script
NUMBERS=”9 7 3 8 37.53“

for number in `echo $NUMBERS` 

# for number in 9 7 3 8 37.53

do     

         echo -n “$number “

done

 

 

 

Operating on all files in the current directory using for loop bash script
Operating on all files in the current directory using for loop bash script

 

Generating the [list] in a for loop with command substitution bash script
Generating the [list] in a for loop with command substitution bash script

 

seq command 

seq command 
seq is a utility for generating a sequence of numbers.
seq [OPTION]… LAST
Command Usage Output
seq 10 1

2

3

4

5

7

8

9

10
seq [OPTION]… FIRST LAST
Command Usage Output
seq 1 5 1

2

3

4

5

 

 

 

seq
seq [OPTION]… FIRST INCREMENT LAST
Command Usage Output
seq  1 2 10 1

3

5

7

9

 

 

 

Multiple ways of sequencing using for loop (including C style also)

Multiple ways to count up to 10 (including C style also)
#!/bin/bash

# Multiple ways to count up to 10.

# Standard syntax.

for a in 1 2 3 4 5 6 7 8 9 10

        do

        echo -n “$a ”

 done

echo

 #!/bin/bash

# Using “seq” …

for a in `seq 10`

do 

       echo -n “$a”

done

#!/bin/bash

# Using ellipsis

for a in {1..10}

        do 

        echo -n  “$a”

        done 

#!/bin/bash

# Now, let’s do the same, using C-like syntax.

LIMIT=10

for ((a=1; a <= LIMIT ; a++)) 

    do 

    echo -n “$a “

done

Note: Output Of all the above scripts are integer values printed from 1 to 10 on the terminal

 

Multiple ways for sequencing using for loop in Bash Scripting
Multiple ways for sequencing using for loop in Bash Scripting

 

C style for loop example in Bash Scripting
C style for loop example in Bash Scripting