How to Add Output "Non_Assigned" When There Is No Match in Grep

How to add output non_assigned when there is no match in grep?

This will do the job:

for p in $(<input.txt)
do
    (COMMAND $p | grep -w "phylum") || echo "non_assigned"
done >> results.txt

This runs the command and the grep in a subshell. If the grep finds 'phylum', the RHS of the || is not run; if 'phylum' is not found, the echo is executed to output a suitable marker.

Notice that the redirection has been moved to after the done; it might be better to use > rather than >> now.

Beware the set option -o pipefail — if the command can fail, you might need to use set +o pipefail. However, it is disabled by default, so you'll probably be OK.

grep a pattern and output non-matching part of line

How about using a combination of grep, sed and $PIPESTATUS to get the correct exit-status?

$ echo Humans are not proud of their ancestors, and rarely invite
  them round to dinner | grep dinner | sed -n "/dinner/s/dinner//p"
Humans are not proud of their ancestors, and rarely invite them round to 

$ echo $PIPESTATUS[1]
0[1]

The members of the $PIPESTATUS array hold the exit status of each respective command executed in a pipe. $PIPESTATUS[0] holds the exit status of the first command in the pipe, $PIPESTATUS[1] the exit status of the second command, and so on.

grep operation with ? pattern

With no flags to indicate the input is a regex, it has no special meaning.

Test:

~$ echo "hello ? world" | grep " ? "
hello ? world

Test with the -q flag:

~$ echo "hello ? world" | grep -q " ? "; echo $?
0

$? holds the exit status of the last command. grep was the last command before echo, and it returns 0 when it matches.

If you try a non-matching string, you'll get:

~$ echo "hello world" | grep -q " ? "; echo $?
1

“How to fix ‘sed + grep no return status when no match’ error in shell”

#!/bin/sh -e

This set's the set -e flag. From posix shell set manual emphasis mine:

-e

When this option is on, if a simple command fails for any of the reasons listed in Consequences of Shell Errors or returns an exit
status value >0, and is not part of the compound list following a
while, until, or if keyword, and is not a part of an AND or OR list,
and is not a pipeline preceded by the ! reserved word, then the shell
shall immediately exit.

From man grep:

Normally the exit status is 0 if a line is selected, 1 if no lines
       were selected, and 2 if an error occurred.

As the command grep in the pipeline inside a command substitution returns a non-zero status:

x=`
  eval sed -n -e '1,"$"p' test.txt  | # will not print any googoog
  grep "googoo" # thus this will return with 1
` # command substitution exit status is the exit status of the last command executed
# the last command executed is grep - so command's substitution exit status is 1
# the exit status of variable assignment is the exit status of the last command executed
# the last command executed is command substitution - it's exit status was 1

The command returns with nonzero status, which terminates your script.

Notes:

• Eval is evil, unneeded there, and using it is bad. Just sed -n -e '1,'"$p" test.txt...
• Using backticks is deprecated. Don't use backticks. Use $( ... ), which looks cleaner, more readable, allows for nesting.
• Remember about -e shell flag. Use it wise and learn to handle exit statuses from commands.

grep return 0 if no match

The actual answer to this question is to add || true to the end of the command, e.g.:

echo thing | grep x || true

This will still output a 0 return code.

Grep and other programs not found in script

$PATH is a special variable to the shell. It defines the list of directories to be searched when executing subcommands.

Bash won't know where grep, awk or chown are. Please use different variable name instead of $PATH.

Try

#!/bin/bash

# Script for getting all TODOS

xPATH="~/documents/obsidian-notes/"
OUTPUT="/home/fish/documents/obsidian-notes/TODO.md"

echo "#TODO" > $OUTPUT

grep -hr --exclude-dir=plugins "\bTODO\b:.*" $xPATH | awk '{print $0,"\n"}' >> $OUTPUT

What is assigned to a variable if 'grep' doesn't return anything?

If grep returns nothing, the $test_avd variable would be empty. But there's no need for a variable here.

Instead of this:

test_avd=$(android list avd | grep test)
if [ ! -z $test_avd ]

Use this:

if android list avd | grep -q test

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Note: when variables are needed, the ! -z is also needless; [ "$test_avd" ] returns exactly the same result as [ ! -z $test_avd ].

grep command always includes html tag with matching output

As per a related question here and use of extended and perl patterns in grep (and egrep). You would have to use a regular expression which returns only the matched group (the text of tag) sth like this (not tested):

grep -oP '<[a-zA-Z]+> \K\[^<]+' test.txt

What the regex above does is return the text of the tag only, as matched group and reject any open close tags

grep extended patterns

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