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${line#*'Caused By'} is a specific case of the variable substitution ${parameter#word} (as it's written in the bash manual, and also in the POSIX standard for the sh shell).

In ${parameter#word}, the pattern word will be removed from the beginning of the value of $parameter. It's called "Remove Smallest Prefix Pattern" because it will remove the shortest matching prefix string that matches the pattern in word (with ## in place of # it removes the longest matching prefix string).

It this specific example, the string Caused by (and anything before it, thanks to the *) is, if it exists, removed from the value of $line. The single quotes around the string are redundant.

By comparing the result of the substitution with the value of the variable itself, the test determines whether the value of $line contains the text Caused by, and prints Yes if it does.

This is equivalent to

if [[ "$line" == *'Caused by'* ]]; then echo 'Yes' fi 

in bash, ksh93 or zsh, or

case "$line" in *'Caused by'*) echo 'Yes' esac 

in any sh shell.

The loop in the question reads "lines" from standard input. See the question "https://unix.stackexchange.com/questions/209123/understand-ifs-read-r-line " for a discussion about this.

${line#*'Caused By'} is a specific instance of the variable substitution ${parameter#word} (as it's written in the bash manual, and also in the POSIX standard for the sh shell).

In ${parameter#word}, the pattern word will be removed from the beginning of the value of $parameter. It's called "Remove Smallest Prefix Pattern" because it will remove the shortest matching prefix string that matches the pattern in word (with ## in place of # it removes the longest matching prefix string).

It this specific example, the string Caused by (and anything before it, thanks to the *) is, if it exists, removed from the value of $line. The single quotes around the string are redundant.

By comparing the result of the substitution with the value of the variable itself, the test determines whether the value of $line contains the text Caused by, and prints Yes if it does.

This has the same effect as

if [[ "$line" == *'Caused by'* ]]; then echo 'Yes' fi 

in bash, ksh93 or zsh, or

case "$line" in *'Caused by'*) echo 'Yes' esac 

in any sh shell.

The loop in the question reads "lines" from standard input. See the question "https://unix.stackexchange.com/questions/209123/understand-ifs-read-r-line " for a discussion about this.

${line#*'Caused By'} is a specific case of the variable substitution ${parameter#word} (as it's written in the bash manual, and also in the POSIX standard for the sh shell).

In ${parameter#word}, the word will be removed from the beginning of the value of $parameter. It's called "Remove Smallest Prefix Pattern" because it will remove the shortest matching prefix string that matches the pattern in word (with ## in place of # it removes the longest matching prefix string).

It this specific example, the string Caused by (and anything before it, thanks to the *) is, if it exists, removed from the value of $line. The single quotes around the string are redundant.

By comparing the result of the substitution with the value of the variable itself, the test determines whether the value of $line contains the text Caused by, and prints Yes if it does.

This is equivalent to

if [[ "$line" == *'Caused by'* ]]; then echo 'Yes' fi 

in bash, ksh93 or zsh, or

case "$line" in *'Caused by'*) echo 'Yes' esac 

in any sh shell.

The loop in the question reads "lines" from standard input. See the question "https://unix.stackexchange.com/questions/209123/understand-ifs-read-r-line " for a discussion about this.

${line#*'Caused By'} is a specific case of the variable substitution ${parameter#word} (as it's written in the bash manual, and also in the POSIX standard for the sh shell).

In ${parameter#word}, the pattern word will be removed from the beginning of the value of $parameter. It's called "Remove Smallest Prefix Pattern" because it will remove the shortest matching prefix string that matches the pattern in word (with ## in place of # it removes the longest matching prefix string).

It this specific example, the string Caused by (and anything before it, thanks to the *) is, if it exists, removed from the value of $line. The single quotes around the string are redundant.

By comparing the result of the substitution with the value of the variable itself, the test determines whether the value of $line contains the text Caused by, and prints Yes if it does.

This is equivalent to

if [[ "$line" == *'Caused by'* ]]; then echo 'Yes' fi 

in bash, ksh93 or zsh, or

case "$line" in *'Caused by'*) echo 'Yes' esac 

in any sh shell.

The loop in the question reads "lines" from standard input. See the question "https://unix.stackexchange.com/questions/209123/understand-ifs-read-r-line " for a discussion about this.

${line#*'Caused By'} is a specific case of the variable substitution ${parameter#word} (as it's written in the bash manual, and also in the POSIX standard for the sh shell).

In ${parameter#word}, the word will be removed from the beginning of the value of $parameter. It's called "Remove Smallest Prefix Pattern" because it will remove the shortest matching prefix string that matches the pattern in word (with ## in place of # it removes the longest matching prefix string).

It this specific example, the string Caused by (and anything before it, thanks to the *) is, if it exists, removed from the value of $line. The single quotes around the string are redundant.

By comparing the result of the substitution with the value of the variable itself, the test determines whether the value of $line contains the text Caused by, and prints Yes if it does.

This is equivalent to

if [[ "$line" == *'Caused by'* ]]; then echo 'Yes' fi 

in bash, ksh93 or zsh, or

case "$line" in *'Caused by'*)  echo 'Yes' esac 

in any sh shell.

${line#*'Caused By'} is a specific case of the variable substitution ${parameter#word} (as it's written in the bash manual, and also in the POSIX standard for the sh shell).

In ${parameter#word}, the word will be removed from the beginning of the value of $parameter. It's called "Remove Smallest Prefix Pattern" because it will remove the shortest matching prefix string that matches the pattern in word (with ## in place of # it removes the longest matching prefix string).

It this specific example, the string Caused by (and anything before it, thanks to the *) is, if it exists, removed from the value of $line. The single quotes around the string are redundant.

By comparing the result of the substitution with the value of the variable itself, the test determines whether the value of $line contains the text Caused by, and prints Yes if it does.

This is equivalent to

if [[ "$line" == *'Caused by'* ]]; then echo 'Yes' fi 

in bash, ksh93 or zsh, or

case "$line" in *'Caused by'*) echo 'Yes' esac 

in any sh shell.

The loop in the question reads "lines" from standard input. See the question "https://unix.stackexchange.com/questions/209123/understand-ifs-read-r-line " for a discussion about this.