Shell Script Linux Substract Parameter Grep

Subtracting strings (that are numbers) in a shell script

You can do basic integer math in bash by wrapping the expression in $(( and )).

$ echo $(( 5 + 8 ))
13

In your specific case, the following works for me:

$ echo "${new_size}-${current_size}"
802-789
$ echo $(( ${new_size}-${current_size} ))
13

Your output at the end is a bit odd. Check that the grep expression actually produces the desired output. If not, you might need to wrap the regular expression in quotation marks.

Subtracting a varibale obtained as output of commands and an integer in shell script

You are getting this error because BASH arithmetic cannot handle floating point numbers and you will get same error while running this command in bash:

((100-93.0))

But you can skip grep, sed and all bash directives. Just a single awk can handle this computation like this:

top -bn1 | awk -F, '/Cpu/ {print 100-$4}'

shell script for grabbing data and subtracting

#!/bin/sh

URL1=http://runescape.com/title.ws
tot=`wget  -qO- $URL1  | grep -i PlayerCount | cut -d\> -f4 | cut -d\< -f1 | sed -e's/,//'`
URL2=http://oldschool.runescape.com
b=`wget -qO- $URL2| grep "people playing" | awk '{print $4}'`
a=`expr $tot - $b`
echo "$a people `date '+%r %b %d %Y'`"

... if you want commas do this add these line to the script ...

export LC_ALL=en_US.UTF-8
a_with_comma=`echo $a | awk "{printf \"%'d\n\", \\$1}"`
echo "$a_with_comma people `date '+%r %b %d %Y'`"

shell script subtract fields from pairs of lines

Using GNU awk:

awk -F '[ -]' '{ map[$2][$3]=$4;print } END { for (i in map) { print i": "(map[i]["stop:"]-map[i]["start:"])" // ("map[i]["stop:"]"-"-map[i]["start:"]")" } }' file

Explanation:

awk -F '[ -]' '{                                                       # Set the field delimiter to space or "-"
                 map[$2][$3]=$4;                                       # Create a two dimensional array with the second and third field as indexes and the fourth field as the value
                 print                                                 # Print the line
               } 
           END { for (i in map) { 
                 print i": "(map[i]["stop:"]-map[i]["start:"])" // ("map[i]["stop:"]"-"-map[i]["start:"]")"                                                      # Loop through the array and print the data in the required format
                 } 
                }' file

Subtracting a number from a variable throwing an error

str=$(grep -w $intron ../file_to_be_grepped_from | awk '{print($2-1)}')
en=$(grep -w $intron ../file_to_be_grepped_from | awk '{print($3+1)}')

Add/subtract variables in a really dumb shell

Another specific solution to your problem (n2 - n1 + 1) based on seq, sort -nr and uniq -u (POSIX-compliant).

foo()
{
    {
        seq 1 "$2"
        seq 0 "$1"
    } \
        | sort -n \
        | uniq -u \
        | grep -n "" \
        | sort -nr \
        | { read num; echo "${num%:*}"; }
}

$ foo 100 2000
1901

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