≡ Menu

arithmetic

You can use find command or recursdir command to recurse through local or remote directories to command/find files or create tar files.

recursdir command pass a C script to recursively perform operations on files. recursdir is an excellent tool for automatic stuff. It provides C style programming functions and statements such as:

  • strncmp()
  • exec()
  • system()
  • strstr()
  • strcat()
  • printf()
  • popen()
  • if ( expr ) { take-action }
  • if ( expr ) { take-action } else { do-something-else; }
  • /* comments */
  • Detecting file types and macros
  • All of the logical, arithmetic and bitwise C operators are supported. These are ( ) >= < = > < != == && || ! - + * / % & ^ and have the same meanings and precedences as in C. etc.

[click to continue…]

With the help of BASH shell and IF command it is possible to find out if file exists or not. Generally, this is known as conditional expressions. Conditional expressions are used by the [[ compound command and the test and [ builtin commands to test file attributes and perform string and arithmetic comparisons. General syntax:

[ parameter FILE ]
OR
test parameter FILE

Where parameter can be any one of the following:

  • -e: Returns true value if file exists
  • -f: Return true value if file exists and regular file
  • -r: Return true value if file exists and is readable
  • -w: Return true value if file exists and is writable
  • -x: Return true value if file exists and is executable
  • -d: Return true value if exists and is a directory

Examples

Find out if file /etc/passwd file exists or not

Type the following commands:
$ [ -f /etc/passwd ] && echo "File exists" || echo "File does not exists"
$ [ -f /tmp/fileonetwo ] && echo "File exists" || echo "File does not exists"

Find out if directory /var/logs exists or not

Type the following commands:
$ [ -d /var/logs ] && echo "Directory exists" || echo "Directory does not exists"
$ [ -d /dumper/fack ] && echo "Directory exists" || echo "Directory does not exists"

You can use conditional expressions in a shell script:

#!/bin/bash
FILE=$1
 
if [ -f $FILE ];
then
   echo "File $FILE exists"
else
   echo "File $FILE does not exists"
fi
 

Save and execute the script:
$ chmod +x script.sh
$ ./script.sh /path/to/file
$ ./script.sh /etc/resolv.conf

You can use this technique to verify that backup directory and backup source directory exits See example script for more information.