File Handling using Shell Scripts

File handling using Shell Scripts

1. to prepend a line to a file
   
2. to develop a temporary file name generator
   
3. to compare two files
   

Requirements:

    Suse Linux, BASH Scripting

Program

(a) Prepending a line to a file

 

#!/bin/bash

# prepend.sh: Add text at beginning of file.

 

E_NOSUCHFILE=65

 

read -p "File: " file   # -p arg to 'read' displays prompt.

if [ ! -e "$file" ]

    then   # Bail out if no such file.

    echo "File $file not found."

    exit $E_NOSUCHFILE

fi

 

read -p "Title: " title

cat - $file <<<$title > $file.new

echo "Modified file is $file.new"

exit 0

 

(b) to develop a temporary file name generator

#!/bin/bash

# tempfile-name.sh:  temp filename generator

BASE_STR=`mcookie`   # 32-character magic cookie.

POS=11               # Arbitrary position in magic cookie string.

LEN=5                # Get $LEN consecutive characters.

prefix=temp          #  This is, after all, a "temp" file.

#  For more "uniqueness," generate the filename prefix

#+ using the same method as the suffix, below.

 

suffix=${BASE_STR:POS:LEN}

# Extract a 5-character string, starting at position 11.

temp_filename=$prefix.$suffix

# Construct the filename.

echo "Temp filename = "$temp_filename""

# sh tempfile-name.sh

# Temp filename = temp.e19ea

exit 0

 

(c) Comparing two files

#!/bin/bash

ARGS=2  # Two args to script expected.

E_BADARGS=65

E_UNREADABLE=66

if [ $# -ne "$ARGS" ]

then

  echo "Usage: `basename $0` file1 file2"

  exit $E_BADARGS

fi

 

if [[ ! -r "$1" || ! -r "$2" ]]

then

  echo "Both files to be compared must exist and be readable."

  exit $E_UNREADABLE

fi

 

cmp $1 $2 &> /dev/null  # /dev/null buries the output of the "cmp" command.

if [ $? -eq 0 ]         # Test exit status of "cmp" command.

then

  echo "File \"$1\" is identical to file \"$2\"."

else  

  echo "File \"$1\" differs from file \"$2\"."

fi

exit 0

 

 

Observation:

Open the VI editor

$: vi <filename>

Compile using bash

$: sh <filename>