Deleting a PARTICULAR word from a file using shell script

shell

Hi I am having a problem in deleting a particular set of words from a file using Shell script. Here goes my problem,
My file: group.dat
Sample lines
ADMIN
ADMINISTRATION
ADMINISTRATOR
My Script: groupdel.sh

#!/bin/sh
groupf="<pathtofile>/group.dat"
tmp="<pathtofile>/te"
delgrp()
{
        echo "Enter the group to be deleted"
        read gname
        echo "-------------------"
        for gn in `cat $groupf`
        do
                if [ "$gname" = "$gn" ]
                then
                        sed -e "s/$gname//g" $groupf > $tmp&&mv $tmp $groupf
                        echo "deleted group"
                        cat $groupf
                        exit 1
                fi
        done
}
echo "Welcome to Group delete wizard"
delgrp

Output:
Enter the group to be deleted

ADMIN

deleted group

ISTRATION
ISTRATOR

Problem: My problem is I dont want the script to delete ADMINISTRATION or ADMINISTRATOR but to delete only ADMIN, any help how to achieve it.
Thanks in Advance

Best Answer

#!/bin/sh
groupf="<pathtofile>/group.dat"
tmp="<pathtofile>/te"
delgrp()
{
    echo "Enter the group to be deleted"
    read gname
    echo "-------------------"
    sed -e "/^$gname[[:blank:]]/d" "$groupf" > "$tmp" && mv "$tmp" "$groupf"
    echo "deleted group $gname"
    cat "$groupf"
    return 0
}
echo "Welcome to Group delete wizard"
delgrp

Assuming that the group name is at the beginning of the line and there are other things on the line and you want to delete the whole line, use the regular expression and command as shown.

There's no need for a loop since sed will iterate over the lines of the file for free.

You should return from a function rather than exit from it. Zero means success. One indicates an error or failure.

Always quote variable names that contain filenames.

Related Solutions

Ruby – How to call shell commands from Ruby

This explanation is based on a commented Ruby script from a friend of mine. If you want to improve the script, feel free to update it at the link.

First, note that when Ruby calls out to a shell, it typically calls /bin/sh, not Bash. Some Bash syntax is not supported by /bin/sh on all systems.

Here are ways to execute a shell script:

cmd = "echo 'hi'" # Sample string that can be used

Kernel#` , commonly called backticks – `cmd`

This is like many other languages, including Bash, PHP, and Perl.

Returns the result (i.e. standard output) of the shell command.

Docs: http://ruby-doc.org/core/Kernel.html#method-i-60
```
value = `echo 'hi'`
value = `#{cmd}`
```
Built-in syntax, %x( cmd )

Following the x character is a delimiter, which can be any character. If the delimiter is one of the characters (, [, {, or <, the literal consists of the characters up to the matching closing delimiter, taking account of nested delimiter pairs. For all other delimiters, the literal comprises the characters up to the next occurrence of the delimiter character. String interpolation #{ ... } is allowed.

Returns the result (i.e. standard output) of the shell command, just like the backticks.

Docs: https://docs.ruby-lang.org/en/master/syntax/literals_rdoc.html#label-Percent+Strings
```
value = %x( echo 'hi' )
value = %x[ #{cmd} ]
```
Kernel#system

Executes the given command in a subshell.

Returns true if the command was found and run successfully, false otherwise.

Docs: http://ruby-doc.org/core/Kernel.html#method-i-system
```
wasGood = system( "echo 'hi'" )
wasGood = system( cmd )
```
Kernel#exec

Replaces the current process by running the given external command.

Returns none, the current process is replaced and never continues.

Docs: http://ruby-doc.org/core/Kernel.html#method-i-exec
```
exec( "echo 'hi'" )
exec( cmd ) # Note: this will never be reached because of the line above
```

Here's some extra advice: $?, which is the same as $CHILD_STATUS, accesses the status of the last system executed command if you use the backticks, system() or %x{}. You can then access the exitstatus and pid properties:

$?.exitstatus

For more reading see:

Bash – How to check if a directory exists in a Bash shell script

To check if a directory exists in a shell script, you can use the following:

if [ -d "$DIRECTORY" ]; then
  # Control will enter here if $DIRECTORY exists.
fi

Or to check if a directory doesn't exist:

if [ ! -d "$DIRECTORY" ]; then
  # Control will enter here if $DIRECTORY doesn't exist.
fi

However, as Jon Ericson points out, subsequent commands may not work as intended if you do not take into account that a symbolic link to a directory will also pass this check. E.g. running this:

ln -s "$ACTUAL_DIR" "$SYMLINK"
if [ -d "$SYMLINK" ]; then 
  rmdir "$SYMLINK" 
fi

Will produce the error message:

rmdir: failed to remove `symlink': Not a directory

So symbolic links may have to be treated differently, if subsequent commands expect directories:

if [ -d "$LINK_OR_DIR" ]; then 
  if [ -L "$LINK_OR_DIR" ]; then
    # It is a symlink!
    # Symbolic link specific commands go here.
    rm "$LINK_OR_DIR"
  else
    # It's a directory!
    # Directory command goes here.
    rmdir "$LINK_OR_DIR"
  fi
fi

Take particular note of the double-quotes used to wrap the variables. The reason for this is explained by 8jean in another answer.

If the variables contain spaces or other unusual characters it will probably cause the script to fail.

ADMIN

Best Answer

Related Solutions

Ruby – How to call shell commands from Ruby

Bash – How to check if a directory exists in a Bash shell script

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