Artikel in Serie "Shells and related Scripting Languages"

Find Files by Size given in Bytes

Some examples:

Find files in current directory that have a size of 400 bytes or more:

sfind -min 400

Find files in /etc that have a size of 50 kilobytes (1 kilobyte = 1024 bytes) or more:

sfind -dir /etc -min 50k

Find files in /var with size between 100 and 500 megabytes, suppress warnings, print sizes in human-readable format:

sfind -dir /var -min 100m -max 500m -quiet -human

Note: Yes, i know, Oracle distributes a tool that is also called „sfind“, but anyway …

Weiterlesen … »

Using sed or awk to ensure a specific last Line in a Text

Given a file containing bytes of text with lines separated by the newline character (\n), one of these lines can be said to be „the last line of the file“; it is a sequence of bytes occurring in the file, for which holds:

  • The sequence contains no newline character, and
  • the sequence is followed by at most one newline character and no other bytes.

The task at hand is, using shell utilities, to write a procedure that makes sure that a given file contains a last line that contains a desired sequence of text characters.

Weiterlesen … »

Make a Bourne Again Shell Script Log its Output to a File

The Bourne Again Shell script presented in this article demonstrates techniques related to capturing and logging output (standard output and standard error stream) of a script into a log file while also delivering it to the regular output destinations (for example the terminal or whatever the caller has chosen to redirect to). Some questions are addressed:

  • How to „clone“ standard output and standard error stream of a shell script to a single log file?
  • Are the messages from both streams interleaved into a single file in the appropriate order?
  • Can a script perform output cloning for some portions of its procedure while skipping it for others?
  • Are there specific requirements for output that is to be cloned to a file?
  • Are there best practices when a script modifies its own output redirections?

The example provided below has been tested on GNU/Linux using GNU „bash“ version 5 and „tee“ version 8.32 from GNU coreutils. It uses the Bash-only feature of process substitution. An implementation in POSIX Shell (possibly using only POSIX tools) would be more difficult.

Weiterlesen … »

Maintaining Multi-Line „stat“ Formats using Bourne Again Shell

The stat command from GNU core utilities features not only a --format FORMAT option but also a --printf FORMAT one, the difference being that the latter allows for backslash escapes such as \n.

This allows for custom per-file report formats containing newlines, for example:

stat --printf 'Name: %n\nSize: %s Bytes\n' /etc/passwd

If the format string becomes more complex, the command line soon becomes unwieldy, such as:

stat --printf 'Name: %n\nOwner ID: %u\nSize: %s Bytes\nLast accessed: %x\n' /etc/passwd

Weiterlesen … »

Print all indented Lines following a non-indented Line

Some configuration and output text formats contain sections like the following:

   value 3

In this article, two scripts are presented that print all consecutive indented lines that follow a non-indented line that matches a search pattern given by a regular expression.

This means, given the single argument foo and the standard input above, the scripts should

  • determine the line that matches foo and
  • print the following two lines, but no other lines.

Also, the indentation of the printed lines should be removed.

Weiterlesen … »