CNIT 340 Strings and Text

what does cut do?

cuts data from a file or piped stdout

what does the paste command do?

puts two lines together

how do you set the delimiter in the paste command?

using the -d option

how is output of cut redirected?

> or |

cut -c only works for fixed length fields (t/f)

true

how can you specify the field number with the cut command?

-f

text and file contents do not need filtering/reformatting before being used (t/f)

false

what are some reformatting/filtering commands

head

tail

grep

tr

sort

uniq

head is a derivative of which basic command?

cat

what does head do?

prints out first n lines of a file to stdout

what is the default value of n in head?

10

what is the syntax of head?

head -n # filename1

ex: head -n /etc/resolv.conf

what is tail a derivative of?

cat

tail is the opposite of what command?

head

what does the head command do?

print out the last n lines of a file to stdout

what is the default value of n in tail?

10

what is the syntax of tail?

tail -n # filename

ex: tail -n /var/log

the tail command supports piping (t/f)

false

what does grep stand for?

globally regular expression print

what does grep do?

sends lines with a regex search term to stdout

what does the tr command mean?

transliterate

what does the tr command do?

translates characters in a standard input stream

how are characters translated in tr command?

with a pipe or < (read input from file)

tr can use regular expressions as parameters (t/f)

true

tr can use octal values of ASCII chars for paramters (t/f)

true

what does the -s option do in the tr command?

replace repeated characters

what does the -d option do in the tr command?

delete charaters

tr cannot use character classes as parameters (t/f)

false

character classes can be thought of as regular expressions (t/f)

true

what are some common character classes?

alpha

lower

upper

digit

alnum

cntrl

punct

what does the sort command do?

reorderrs lines in alphabetical order

does uppercase or lowercase come first in the output of a sort command?

uppercase

what does the -u option do for the sort command?

removes all duplicate entires in the output

what does the -n option do for the sort command?

sorts a numeric list

what does the -r option do for the sort command?

sorts the list in reverse order

what does uniq command do?

removes consecutive repeated lines

uniq can provide a count of unique words (t/f)

true

what are the two methods for string processing?

expr

${}

expr is an external command (t/f)

false, it is internal

${} is internal to the bash shell (t/f)

true

what will return the length of the string?

${#}

what will return the number of elements in an array?

${#VAR[@] }

what will return the remaining substring of a string as a specific position?

${:}

what will return teh substring of string length at a specific position?

${::}

what does ${#} do?

returns the SHORTEST match of substring from the FRONT of string

what does ${##} do?

returns the LONGEST match of substring from the FRONT of string

what does ${%} do?

returns SHORTEST match of substring form the BACK of string

what does ${%%} do?

returns the LONGEST match of substring from the BACK of string

what does ${//} do?

returns string with the FIRST match of substring replaced by replacement

what does ${///} do?

return string with ALL matches of substring replaced by replacement

what does ${/#/} do?

if substring matches the FRONT of string, return string with substring replaced by replacement

what does ${/%/} do?

if substring matches the BACK of string, return string with substring replaced by replacement

what does expr match do

returns the length of the matching at the beginning of

what does expr index do

returns position in string of the first char of matching substring

what does expr substr do

returns length characters from string starting at position

bash supports regex comparison (match) operator =~ in what type of test?

double bracket [ [ ] ]

when using BASH built in REGEX functions, you can extract strings with () (t/f)

true

BASH_REMATCH is an arry (t/f)

true

what happens if BASH_REMATCH has no index?

reuslt of all matches put together