TOPIC: UNIX SHELLS
Unzipping more than one file at a time in Linux and macOS
10th September 2024To me, it sounded like a task for shell scripting, but I wanted to extract three zip archives in one go. They had come from Google Drive and contained different splits of the files that I needed, raw images from a camera. However, I found a more succinct method than the line of code that you see below (it is intended for the BASH shell):
for z in *.zip; do; unzip "$z"; done
That loops through each file that matches a glob string. All I needed was something like this:
unzip '*.zip'
Without embarking on a search, I got close but have not quoted the search string. Without the quoting, it was not working for me. To be sure that I was extracting more than I needed, I made the wildcard string more specific for my case.
Once the extraction was complete, I moved the files into a Lightroom Classic repository for working on them later. All this happened on an iMac, but the extraction itself should work on any UNIX-based operating system, so long as the shell supports it.
String replacement in BASH scripting
28th April 2023During creation of new posts for a Hugo deployed website, I found myself using the same directories again and again. Since I invariably ended up making typing mistakes when I did so, I fancied the idea of using shortcodes instead.
Because I wanted to turn the shortcode into the actual directory name, I chose the use of text replacement in BASH scripting. Thankfully, this is simple and avoids the use of regular expressions, which can bring their own problems. The essential syntax is as follows:
variable="${variable/search text/replacement}"
For the variable, the search text is substituted with the replacement straightforwardly. It is even possible to include the search and replacement text in variables. In the example below, this is achieved using variables called original and replacement.
variable="${variable/$original/$replacement}"
Doing this got me my translatable shortcodes and converted them into actual directory names for the hugo command to process. There may be other uses yet.
Searching file contents using PowerShell
25th October 2018Having made plenty of use of grep on the Linux/UNIX command and findstr on the legacy Windows command line, I wondered if PowerShell could be used to search the contents of files for a text string. Usefully, this turns out to be the case, but I found that the native functionality does not use what I have used before. The form of the command is given below:
Select-String -Path <filename search expression> -Pattern "<search expression>" > <output file>
While you can have the output appear on the screen, it always seems easier to send it to a file for subsequent use, and that is what I am doing above. The input to the -Path switch can be a filename or a wildcard expression, while that to the -Pattern can be a text string enclosed in quotes or a regular expression. Given that it works well once you know what to do, here is an example:
Select-String -Path *.sas -Pattern "proc report" > c:\temp\search.txt
The search.txt file then includes both the file information and the text that has been found for the sake of checking that you have what you want. What you do next is up to you.
Reloading .bashrc within a BASH terminal session
3rd July 2016BASH is a command-line interpreter that is commonly used by Linux and UNIX operating systems. Chances are that you will find yourself in a BASH session if you start up a terminal emulator in many of these, though there are others like KSH and SSH too.
BASH comes with its own configuration files and one of these is located in your own home directory, .bashrc. Among other things, it can become a place to store command shortcuts or aliases. Here is an example:
alias us='sudo apt-get update && sudo apt-get upgrade'
Such a definition needs there to be no spaces around the equals sign, and the actual command to be declared in single quotes. Doing anything other than this will not work, as I have found. Also, there are times when you want to update or add one of these and use it without shutting down a terminal emulator and restarting it.
To reload the .bashrc file to use the updates contained in there, one of the following commands can be issued:
source ~/.bashrc
. ~/.bashrc
Both will read the file and execute its contents so you get those updates made available so you can continue what you are doing. There appears to be a tendency for this kind of thing in the world of Linux and UNIX because it also applies to remounting drives after a change to /etc/fstab and restarting system services like Apache, MySQL or Nginx. The command for the former is below:
sudo mount -a
Often, the means for applying the sorts of in-situ changes that you make are simple ones too, and anything that avoids system reboots has to be good since you have less work interruptions.
Using Korn shell commands in scripts running under the bash shell
19th May 2007This is actually a fairly simple one: just prefix the relevant command with ksh like below (in the example below, bash won't know what to do with the print command otherwise):
ksh print "Hello, world!"
It's also useful for running Korn shell scripts under the bash shell as well.
Recalling previous commands in the Korn shell
18th May 2007The default shell on Solaris boxes seems to be Korn and the version that I have encountered doesn't appear to allow obvious access to the command history. In the bash shell, the up and down cursor keys scroll through your command history for you, but Korn doesn't seem to allow this. Thankfully, there is another way: you can set up the editor vi as the default method for gaining access to the command history by adding the following line to the .profile file in your home directory:
set -o vi
Then, you can use the Vi (it's pronounced vee-eye, apparently) commands ESC+h and ESC+j to move up and down the list of previous commands. That, or, assuming that you have access to it, just use the bash shell anyway...