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How I use Bash to automate tasks on Linux Jim Hall Tue, 07/26/2022 - 03:00 1 reader likes this 1 reader likes this

The Bash command line is a great way to automate tasks. Whether you are running Linux on a server and need to manipulate log files or other data, or you're a desktop user who just wants to keep files tidy, you can use a few automation features in Bash to make your work easier.

Linux for command: Automate tasks on a files

If you have a bunch of files to work on at once, and you need to do the same thing with every file, use the for command. This command iterates across a list of files, and executes one or more commands. The for command looks like this:

for variable in list
do
    commands
done

I've added some extra spacing in there to help separate the different parts of the for command. That multi-line command might look difficult to run on the command line, but you can use ; to put everything on one line, like this:

for variable in list ; do commands ; done

Let's see it in action. One way I use the for command is to rename a bunch of files. Most recently, I had a bunch of screenshots that I wanted to rename. The screenshots had names like filemgr.png or terminal.png and I wanted to put screenshot before each name instead. I ran a single for command to rename thirty files at once. Here's an example with just two files:

$ ls
filemgr.png  terminal.png
$ for f in *.png ; do mv $f screenshot-$f ; done
$ ls
screenshot-filemgr.png  screenshot-terminal.png

The for command makes it easy to perform one or more actions on a set of files. You can use a variable name that is meaningful to you, such as image or screenshot, or you can use a "shorthand" variable like f, as I did in my example. When I write scripts that use a for loop, I try to use meaningful variable names. But when I'm using for on the command line, I'll usually use a short variable name like f for files or d for directories.

Whatever name you choose for your variable, be sure to reference the variable using $ in the command. This expands the variable to the name of the file you are acting on. Type help for at your Bash prompt to learn more about the for command.

More Linux resources Linux commands cheat sheet Advanced Linux commands cheat sheet Free online course: RHEL technical overview Linux networking cheat sheet SELinux cheat sheet Linux common commands cheat sheet What are Linux containers? Our latest Linux articles Linux conditional execution (if)

Looping across a set of files with for is helpful when you need to do the same thing with every file. But what if you need to do something different for certain files? For that, you need conditional execution with the if statement. The if statement looks like this:

if test
then
    commands
fi

You can also do if/else tests by using the else keyword:

if test
then
    commands
else
    commands
fi

For more complicated processing, you can use if/else-if/else evaluations. I might use this in a script, when I need to automate a job to process a collection of files at once:

if test
then
    commands
elif test2
then
    commands
elif test3
then
    commands
else
    commands
fi

The if command allows you to perform many different tests, such as if a file is really a file, or if a file is empty (zero size). Type help test at your Bash prompt to see the different kinds of tests you can use in an if statement.

For example, let's say I wanted to clean up a log directory that had several dozen files in it. A common task in log management is to delete any empty logs, and compress the other logs. The easiest way to tackle this is to just delete the empty files. There isn't an if test that exactly matches that, but we have -s file to test if something is a file, and if the file is not empty (it has a size). That's the opposite of what we want, but we can negate the test with ! to see if something is not a file or is empty.

Let's look at an example to see this at work. I've created two test files: one is empty, and the other contains some data. We can use if to print the message "empty" if the file is empty:

$ ls
datafile  emptyfile
$ if [ ! -s datafile ] ; then echo "empty" ; fi
$ if [ ! -s emptyfile ] ; then echo "empty" ; fi
empty

We can combine this with for to examine a list of log files to delete the empty files for us:

$ ls -l
total 20
-rw-rw-r--. 1 jhall jhall 2 Jul  1 01:02 log.1
-rw-rw-r--. 1 jhall jhall 2 Jul  2 01:02 log.2
-rw-rw-r--. 1 jhall jhall 2 Jul  3 01:02 log.3
-rw-rw-r--. 1 jhall jhall 0 Jul  4 01:02 log.4
-rw-rw-r--. 1 jhall jhall 2 Jul  5 01:02 log.5
-rw-rw-r--. 1 jhall jhall 0 Jul  6 01:02 log.6
-rw-rw-r--. 1 jhall jhall 2 Jul  7 01:02 log.7
$ for f in log.* ; do if [ ! -s $f ] ; then rm -v $f ; fi ; done
removed 'log.4'
removed 'log.6'
$ ls -l
total 20
-rw-rw-r--. 1 jhall jhall 2 Jul  1 01:02 log.1
-rw-rw-r--. 1 jhall jhall 2 Jul  2 01:02 log.2
-rw-rw-r--. 1 jhall jhall 2 Jul  3 01:02 log.3
-rw-rw-r--. 1 jhall jhall 2 Jul  5 01:02 log.5
-rw-rw-r--. 1 jhall jhall 2 Jul  7 01:02 log.7

Using the if command can add some intelligence to scripts, to perform actions only when needed. I often use if in scripts when I need to test if a file does or does not exist on my system, or if the entry the script is examining is a file or directory. Using if allows my script to take different actions as needed.

Bash has a few handy automation features that make my life easier when working with files on Linux.

Image by:

Opensource.com

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Shrink PDFs with this Linux tool Howard Fosdick Tue, 07/26/2022 - 03:00 1 reader likes this 1 reader likes this

Excluding HTML, PDF files are probably the most popular document format on the web. Unfortunately, they're not compact. For example, I like to download free eBooks. A quick glance at my eBook directory shows that its 75 PDF files consume about 500 megabytes. On average, that's over 6.6 MB for each PDF file.

Couldn't I save some storage space by compressing those files? What if I want to send a bundle of them through email? Or host them for download on a website? The transmission would be faster if these files were made smaller. This article shows a simple way to reduce PDF file size. The benefit is that it shrinks your PDFs transparently without altering the data content in any way. Plus, you can also compact many PDF files with a single command.

Compare this to the alternatives. You could upload your PDF files to one of the many online file compression websites. Several are free, but you risk the privacy of your documents by uploading them to an unknown website. More importantly, most websites shrink PDFs by tampering with the images they contain. They either change their resolution or their sizes. So you trade lower image quality to get smaller PDF files. That's the same trade-off you face using interactive apps like LibreOffice, or Ghostscript line commands like gs and ps2pdf. The technique we'll illustrate in this article compacts PDFs without altering either the images they contain or their data content. And you can reduce many PDFs with a single line command. Let's get started.

Identify and delete big unused PDFs on Linux

Before you spend time and effort compacting PDF files, identify your largest ones and delete those you don't need. This command lists the 50 biggest PDFs in its directory tree, ordered by descending size:

$ find  -type f  -exec  du -Sh {} +  |  grep .pdf | sort -rh  |  head -n 50

From the output, you can easily identify and eliminate duplicates. You can also delete obsolete files. Getting rid of these space hogs yields big benefits. Now you know which PDFs are the high payback candidates for the reduction technique we'll now cover.

More Linux resources Linux commands cheat sheet Advanced Linux commands cheat sheet Free online course: RHEL technical overview Linux networking cheat sheet SELinux cheat sheet Linux common commands cheat sheet What are Linux containers? Our latest Linux articles Transparently compact PDFs

We'll use the open source Minuimus program to compact PDFs. Minuimus is a generalized command-line utility that performs all sorts of useful file conversions and compressions. To shrink PDFs, Minuimus unloads and then rebuilds them, gaining numerous efficiencies along the way. It does this transparently, without altering your data in any way.

To use Minuimus, download its zip file. Then install it as its documentation explains, with these commands:

$ make deps      # Installs all required supporting packages
$ make all       # Compiles helper binaries
$ make install   # Copies all needed files to /usr/bin

Minuimus is a Perl script, so you run it like this:

$ minuimus.pl  input_file.pdf    # replaces the input file with compressed output

When it runs, Minuimus immediately makes a backup of your original input file. It only replaces the input file with its compacted version after it fully verifies data accuracy by comparing before and after bitmaps representing the data.

A big benefit to Minuimus is that it validates any PDF file it works on. I've found that it gives intelligent, helpful error messages if it encounters any problems. For example, on one of my computers, Minuimus said that it couldn't properly invoke a utility it uses called leanify. Yet it still shrunk the PDFs and ran to successful completion.

Here's how to compact many files in one command. This compresses all the PDF files in a directory:

$ minuimus.pl *.pdf

If you have lots of PDFs to convert, Minuimus might process for a while. So if you're converting hundreds of PDFs, for example, you might want to run Minuimus as a background job. Schedule it for off-hours through your GUI scheduler or as a Cron job.

Be sure to redirect its output from the terminal to files so that you can easily review it later:

$ minuimus.pl *.pdf  1>output_messages.txt  2>error_messages.txtHow much space will you reclaim?

Unfortunately, there's no way to predict how much space Minuimus can save. That's because PDFs contain anything from text to images of all different kinds. They vary enormously. I ran Minuimus on my download directory of PDF books. The directory contained 75 PDFs consuming about 500 MB. Minuimus reduced it by about 11%, to about 445 MB. That's impressive for an algorithm that doesn't change the data.

Across a large group of PDFs, size reduction of 10% to 20% appears common. The biggest files often shrink the most. Processing a collection of big PDFs often reclaims much more space than processing many small PDFs. Some PDF files show really dramatic space savings. That's because some applications create absolutely hideous PDFs. I call those files "PDF monsters." You can slay them with a single Minuimus command.

For example, while writing this article, Minuimus knocked an 85 megabyte PDF down to 32 meg. That's just 38% of its original size. The program slimmed several other monsters by 50%, recovering tens of megabytes. This is why I began this article by introducing a command to list your biggest PDF files. If Minuimus identifies a few monsters you can slay, you can reclaim major disk space for free.

Shrink PDFs with Minuimus

PDF files are useful and ubiquitous. But they often consume a good deal of storage space. Minuimus makes it easy to reduce PDF storage space by 10% to 20% without altering the data. Perhaps its biggest benefit is identifying and transforming malformed "PDF monsters" into smaller, more manageable files.

Minuimus is an open source program used to reduce PDF storage space by 10% to 20% without altering the data.

Linux What to read next Shrink PDF size with this command line trick This work is licensed under a Creative Commons Attribution-Share Alike 4.0 International License. Register or Login to post a comment.

The post How to Work with PDF Files Using ONLYOFFICE Docs in Linux first appeared on Tecmint: Linux Howtos, Tutorials & Guides .

Those Linux users who deal with PDF files have plenty of programs to choose from. More precisely, there exist a great number of dedicated PDF tools that can be used for various tasks. For

The post How to Work with PDF Files Using ONLYOFFICE Docs in Linux first appeared on Tecmint: Linux Howtos, Tutorials & Guides.

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