CEST-CE Term_2 GNU/LINUX (Week 3)

Searching for Files

• To search for files, use the find command, which finds files by name, unlike fgrep, which looks for text inside files.
• find can search for files by name, size, owner, modification date, and more.

Five Common Ways to Use the find Command

• find [startdir…] -print: finds all pathnames under the specified directory.
• find [startdir…] -name ‘basename’ -print: finds pathnames with a specific basename.
• find [startdir…] -user ‘userid’ -print: finds pathnames owned by a specific user.
• find [startdir…] -mtime -30 -print: finds pathnames modified within the last 30 days.
• find [startdir…] -size +100M -print: finds pathnames with a size greater than 100MB.

Using Multiple Expressions with find

• You can use multiple expressions with find to narrow down the search results.
• The pathnames found must meet all the conditions of the expressions used.

Showing Detailed Output with -ls

• The -ls expression with find displays detailed attribute information about the pathnames.
• This is similar to using ls -dils on the displayed names.

Examples of Using find

• find /usr/bin -name '*sh': finds pathnames under /usr/bin ending with sh.
• find /usr/bin -type f -size +2M: finds pathnames under /usr/bin with a size greater than 2MB.
• find /tmp -maxdepth 1 -user student -type d: finds directories under /tmp owned by the student user.

Using fgrep on the Output of find

• You can pipe the output of find to fgrep to search for specific patterns in the pathname output.
• find /usr/bin | fgrep 'sh': finds pathnames under /usr/bin containing the string sh.

Finding Files Using locate or slocate

• The locate or slocate commands search a saved database of pathnames for quick lookup.
• These commands are faster than find for searching for files that have been indexed in the database.

Introduction to Redirection

• Shell redirection allows changing where commands read input and send output, applying to all commands run by the shell.

Redirection of Input and Output

• Input and output can be redirected to or from a file using '' or to or from a program using '|'.
• Redirection allows changing input/output streams of commands.

Output Redirection

• Commands produce standard output and standard error, which can be redirected separately.
• Standard output can be redirected to a file or another command using '>'.
• Standard error is output in case of an error and can be redirected using '2>'.
• '2>' redirects standard error to a file.

Output Redirection Syntax with >

• '>' symbol indicates output redirection to a file, truncating it if it exists.
• Space before '>' is required, and the space after is optional.
• Output redirection is done before running the command.

Rules for Output Redirection

• Redirection only affects visible output.
• Redirection goes to one place.
• By default, only standard output is redirected.

Appending to Files using >>

• '>>' appends output to a file instead of truncating it.
• Used to append output to a file without overwriting existing content.

Additional Notes on Redirection

• Avoid redirecting both stdout and stderr to the same file to prevent overwriting.
• '2>&1' redirects both stdout and stderr safely into a single file.

Input Redirection

• Commands read input from files or standard input (stdin) if no file names are given.
• Redirection using '<' symbol allows reading input from a file.
• Input redirection allows changing input streams of commands.