[bash] Extract characters before marker from all lines in a file with sed

Using sed, it is possible to quickly extract all characters before a given marker from all lines in a file with:

sed 's/MARKER.*//' file.txt

[Linux] Text handling for counting and replacing words

Here is a list of handy commands for VI and SED to count and replace text in a file. For both editors the escape character is /:

VI:

- count total words:

 :%s/\i\+/&/gn    

- count occurrences of particular word:

 :%s/WORD/&/gn    

SED:

- copy all text from marker until end of file:

 sed -n -n '/MARKER/,$p' in >> out  

- replace all occurrences of SOURCE to TARGET with optional characters before SOURCE:

 sed -E 's/(OPTIONAL)?SOURCE/\1TARGET/g' in >> out