PDFcomp: A PDF comprimer easy script

Question

I developed this script in dead time to be able to compress the PDFs that they send me to university and also to be able to send scans to the various institutions that require formats that do not weigh more than 2Mb.

github link: https://github.com/NF02/pdfcomp

#!/bin/sh
#- Function -#
command_exists() {
  command -v "$@" >/dev/null 2>&1
}

pdfcomprimer(){
    gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=$comp -dNOPAUSE \
        -dQUIET -dBATCH -sOutputFile=$pdfOut $pdfIn
}
pdfcomprimerPrev() {
    echo $pdfIn
    if [[ $pdfIn == "" ]]; then
    echo "Missing input files, try again!"
    exit -1
    fi
    while [ "$con" != "quit" ]
      do
        cat << 'EOF'
 ___________ _____________________________________________________________
|  Quality  | Description                                                 |
|-----------|-------------------------------------------------------------|
| screen    | The output file will have up to 72 DPI.                     |
| ebook     | The output file will have up to 150 DPI.                    |
| preprint  | The output file will have up to 300 DPI.                    |
| printer   | The output files will have up to 300 DPI and will be ready  |
|           | for printing                                                |
| default   | It depends on which of the above options is assigned as the |
|           | “default”.                                                  |
| quit      | Close the program                                           |
|           |                                                             |
 -------------------------------------------------------------------------
EOF
        echo "Select the degree of compression: "
        read con
        if [[ $con == "quit" ]]; then
            exit 0
        fi
    
        if [[ $con == "" ]];then
           con="default"
        fi
           
            gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=$comp -dNOPAUSE \
           -dQUIET -dBATCH -sOutputFile=/tmp/prev.pdf $pdfIn
    if [[ $con == "screen" ]] || [[ $con == "ebook" ]] || [[ $con == "preprint" ]] || [[ $con == "print" ]] || [[ $con == "default" ]]; then
        echo "
 ____________________ _____________________________________ ___________________
|  Source file       |          output file                | Compression level |
 ------------------------------------------------------------------------------
  $(du -sh $pdfIn)        $(du -sh /tmp/prev.pdf)                 $con           
 ==============================================================================
    "   
        else echo "format not found"
    fi

    
    done
    exit 0
}

if ! command_exists gs; then
    echo "ghostscript is not installed"
    exit -1
fi

#-  -#
comp="/default"
pdfIn=$1
pdfOut=$2

if [[ $1 == "-fl" ]] || [[ $1 == "--format-list" ]];then
    cat << 'EOF'
 ___________ _____________________________________________________________
|  Quality  | Description                                                 |
|-----------|-------------------------------------------------------------|
| screen    | The output file will have up to 72 DPI.                     |
| ebook     | The output file will have up to 150 DPI.                    |
| preprint  | The output file will have up to 300 DPI.                    |
| printer   | The output files will have up to 300 DPI and will be ready  |
|           | for printing                                                |
| default   | It depends on which of the above options is assigned as the |
|           | “default”.                                                  |
|           |                                                             |
 -------------------------------------------------------------------------
EOF
    exit 0
fi

if [[ $1 == --help ]] || [[ $1 == -h ]] || [[ $1 == -HELP ]] || [[ $1 == "" ]]; then
    cat << 'EOF'
┏━┓╺┳┓┏━╸┏━╸┏━┓┏┳┓┏━┓   ┏━┓ ╺┓
┣━┛ ┃┃┣╸ ┃  ┃ ┃┃┃┃┣━┛   ┃┃┃  ┃
╹  ╺┻┛╹  ┗━╸┗━┛╹ ╹╹     ┗━┛╹╺┻╸
This application allows you to compress PDFs, using ghostscript, this script
is designed to simplify and speed up the use of the tool, making it more 
user-friendly and practical.
----------------------------------------------------------------------------
-                               commands                                   -
----------------------------------------------------------------------------
-h  (--help): shows help on screen, with all passable parameters.
-f  (--format): allows you to select the compression level
-fl (--format-list): shows the list of possible compression levels.
EOF
    exit 0
fi

if [[ $1 == "-f" ]] || [[ $1 == "--format" ]];then
    pdfIn=$3
    pdfOut=$4
    if [[ $2 == "screen" ]] || [[ $2 == "ebook" ]] || [[ $2 == "preprint" ]] ||
        [[ $2 == "print" ]] || [[ $con == "default" ]]; then
        comp="/$2"
        else echo "format not exists" && exit -4
    fi
fi
if [[ $1 == "-p" ]] || [[ $1 == "--prev" ]]; then
    pdfIn=$2
    pdfcomprimerPrev
fi
   
if [[ $pdfIn == "" ]] || [[ $pdfOut == "" ]]; then
    echo "Missing input/output files, try again!"
    else if  [[ $pdfIn == $pdfOut ]];then
        echo "You can't overwrite this file"
        else if test -f "$pdfIn"; then
                pdfcomprimer
            else echo "Input file not exists"
        fi
    fi
fi

Answer 1

Here are a few advices.

Indentation

The "if/else/fi" block such as:

    if [[ $2 == "screen" ]] || [[ $2 == "ebook" ]] || [[ $2 == "preprint" ]] ||
        [[ $2 == "print" ]] || [[ $con == "default" ]]; then
        comp="/$2"
        else echo "format not exists" && exit -4
    fi

would probably be easier to read if is was written as:

    if [[ $2 == "screen" ]] || [[ $2 == "ebook" ]] || [[ $2 == "preprint" ]] ||
        [[ $2 == "print" ]] || [[ $con == "default" ]]; then
        comp="/$2"
    else
        echo "format not exists" && exit -4
    fi

This is even more relevant for the last part of the code:

if [[ $pdfIn == "" ]] || [[ $pdfOut == "" ]]; then
    echo "Missing input/output files, try again!"
    else if  [[ $pdfIn == $pdfOut ]];then
        echo "You can't overwrite this file"
        else if test -f "$pdfIn"; then
                pdfcomprimer
            else echo "Input file not exists"
        fi
    fi
fi

which should/could be rewritten as:

if [[ $pdfIn == "" ]] || [[ $pdfOut == "" ]]; then
    echo "Missing input/output files, try again!"
else
    if  [[ $pdfIn == $pdfOut ]];then
        echo "You can't overwrite this file"
    else
        if test -f "$pdfIn"; then
            pdfcomprimer
        else
            echo "Input file not exists"
        fi
    fi
fi

or even better, using the elif keyword:

if [[ $pdfIn == "" ]] || [[ $pdfOut == "" ]]; then
    echo "Missing input/output files, try again!"
elif  [[ $pdfIn == $pdfOut ]];then
    echo "You can't overwrite this file"
elif test -f "$pdfIn"; then
    pdfcomprimer
else
    echo "Input file not exists"
fi

Consistency

Various stylistic parts of the code are inconsistent:

• indentation is 2 or 4 spaces
• there is 0 or 1 whitespace before brackets ("{")

Write/reuse functions

You've defined small functions such as command_exists ans this is a great idea.

I think you can define even more functions, in particular to deal with output to the user. These huge wall of texts make the actual logic in the code harder. Also, one of the literal string is duplicated making things harder to maintain.

Here is a suggestion:

show_format_resolution() {
    cat << 'EOF'
 ___________ _____________________________________________________________
|  Quality  | Description                                                 |
|-----------|-------------------------------------------------------------|
| screen    | The output file will have up to 72 DPI.                     |
| ebook     | The output file will have up to 150 DPI.                    |
| preprint  | The output file will have up to 300 DPI.                    |
| printer   | The output files will have up to 300 DPI and will be ready  |
|           | for printing                                                |
| default   | It depends on which of the above options is assigned as the |
|           | “default”.                                                  |
| quit      | Close the program                                           |
|           |                                                             |
 -------------------------------------------------------------------------
EOF
}

show_help() {
    cat << 'EOF'
┏━┓╺┳┓┏━╸┏━╸┏━┓┏┳┓┏━┓   ┏━┓ ╺┓
┣━┛ ┃┃┣╸ ┃  ┃ ┃┃┃┃┣━┛   ┃┃┃  ┃
╹  ╺┻┛╹  ┗━╸┗━┛╹ ╹╹     ┗━┛╹╺┻╸
This application allows you to compress PDFs, using ghostscript, this script
is designed to simplify and speed up the use of the tool, making it more 
user-friendly and practical.
----------------------------------------------------------------------------
-                               commands                                   -
----------------------------------------------------------------------------
-h  (--help): shows help on screen, with all passable parameters.
-f  (--format): allows you to select the compression level
-fl (--format-list): shows the list of possible compression levels.
EOF
}

Another function which could be useful would be a function checking whether a format is valid.

Indeed, you have:

    if [[ $con == "screen" ]] || [[ $con == "ebook" ]] || [[ $con == "preprint" ]] || [[ $con == "print" ]] || [[ $con == "default" ]]; then

and then:

    if [[ $2 == "screen" ]] || [[ $2 == "ebook" ]] || [[ $2 == "preprint" ]] ||
        [[ $2 == "print" ]] || [[ $con == "default" ]]; then

and I suspect the second last check of the latter is actually wrong.

Checking the error code of echo

I'm not sure to get the point of doing echo "format not exists" && exit -4. In the case where echo would fail, your script would not exit which is probably not the desired behavior. You could write: echo "format not exists"; exit -4.

Argument management

The way pdfIn and pdfOut get assigned $1 and $2 only to be reassigned in almost all useful cases makes things pretty confusing.

Also, it may be worth providing the values explicitly to pdfcomprimerPrev and pdfcomprimer instead of relying on global variables.

Switch case

Various parts of the logic relying on if and various checks could be written in a more concise way using the case/esac statement.