cut.1posix -f1 -d: /etc/passwd
cut out selected fields of each line of a file
-f  list
       Cut  based  on a list of fields, assumed to be separated in the file by a delimiter character (see
       -d). Each selected field shall be output. Output fields shall be separated by a single  occurrence
       of  the  field delimiter character. Lines with no field delimiters shall be passed through intact,
       unless -s is specified. It shall not be an error to select fields not present in the input line.
-d  delim
       Set the field delimiter to the character delim. The default is the <tab>.
source manpages: cut