How to check if a file is sourced in Bash

Sometimes you will want to ensure that a file is sourced instead of executed. This ensures, among other things, that any environment variables that the script defines remain in your current shell after the script completes.

To do so, use the following to check whether the file was sourced or run in a sub-shell

(return 0 2/dev/null) && sourced=1 || sourced=0
echo "sourced=$sourced"

Bash allows return statements only from functions and in a scripts top level scope IF it → Continue reading “How to check if a file is sourced in Bash”

Pruning directories from find

I have no idea why, but for some reason I always have a hard time remembering the exact syntax for find when I want to prune some list of directories from a search.

Let’s say that you want to execute a find in a directory where there are a lot of .git directories and you don’t want to search through the guts of the repo directories. With the following command we specify the prune predicate ahead of the search for → Continue reading “Pruning directories from find”

Using cut with a delimiter of any amount of whitespace

The TLDR; is to first use tr to replace all occurrences of any horizontal whitespace character with a single space, and then squeeze down any number of spaces to a single space and then define the delimiter for cut as a single space. The following example assumes that you want to see from the 5th column to the end of the line.

<do-something-to-generate-input| tr '[:blank:]' ' ' | tr -s ' ' | cut -d ' ' -f5-

The → Continue reading “Using cut with a delimiter of any amount of whitespace”

Using fc to Edit and Re-execute Bash Commands

I recently learned about the Bash built-in fc. It is a great tool that enables you to edit and re-execute commands from your bash history.

Oftentimes there is a command in your history that instead of just grepping through the history and then re-executing as-is you’ll want to make a modification or two. With fc you can first edit it in your favorite editor and then when closing the editor fc will execute the command.

For me, vim is my → Continue reading “Using fc to Edit and Re-execute Bash Commands”

Flush Commands to BASH History Immediately

I cannot take credit for figuring this one out. Original post is here.

TLDR; is to add the following to your ~/.bashrc

export PROMPT_COMMAND='history -a'

Following are the history configs that I use

######################################################################
shopt -s histappend
HISTSIZE=-1
HISTFILESIZE=-1
HISTCONTROL=ignoreboth
HISTTIMEFORMAT="[%F %T] "
export PROMPT_COMMAND='history -a'
######################################################################
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Configuring rsyslog to rotate log files from log messages streamed to it from a Systemd service

In general, I have moved to writing all of my applications to write their log output to STDOUT. This makes running them on the command line, in an IDE, on a bare metal box, VM, or in a container completely decoupled from how you store and view the logs. No more having multiple logging configs for each flavor of deployment.

In this particular case, I am running an application in a container (but it isn’t necessary that it is in → Continue reading “Configuring rsyslog to rotate log files from log messages streamed to it from a Systemd service”

Looping Through a List of Files with Spaces in the File Name with Bash

If you have a list of files that you want to operate on in a loop in bash and some of them have spaces in the file name the default IFS (Internal Field Separator) will match with the space and tokenize the file.

The simple approach is to temporarily set the IFS as follows.  This can be done in a shell script, but the following example is directly on the command line for ‘one-liner’ usage.

OIFS="$IFS"

IFS=$'\n' 

for i in 
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How To Remove the Byte Order Mark (BOM) from UTF-8 Encoded Text Files

The easiest way that I have seen so far for doing so is to use tail and simply read everything except the first three bytes (start reading at the 4th byte), as follows:

tail --bytes=+4 text_file.txt text_file-wo-bom.txt
Continue reading “How To Remove the Byte Order Mark (BOM) from UTF-8 Encoded Text Files”

Adding the Contents of a Source File to the Beginning of a Target File

Following is *nix a command that you can use to add the contents of a source text file to the start of another text file (the source file).

echo -e '0r <source_file_name\nw' | ed -s <target_file_name
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