Cyberops bash notes

$ type -t cat # identify what the argument is
file

# compgen lists what commands (-c), keywords (-k), and built-ins (-b) are available
$ compgen -k
if
then
else
elif
fi
case
esac
...

$ program < input.txt > output.out

$ program 2> err.msgs

$ program < input.txt > output.out 2> err.msgs

$ program < input.txt > output.out 2>&1
# shorthand
$ program < input.txt &> output.out

$ program < input.txt > /dev/null

$ program < input.txt | tee results.out # the -a option allows tee to append to the file

$ program < input.txt >> appended.file

$ program < input.txt &>> appended.file

$ ping 10.20.30.40 > ping.log &

$ ping 10.20.30.40 &> ping.log &

$ ping 192.168.10.56 &> ping.log &
[1] 7452
$ jobs
[1]+  Running                 ping 192.168.10.56 &> ping.log &
$ fg 1
ping 192.168.10.56 &> ping.log
^C

$ ping 192.168.10.56 &> ping.log &
[1] 7572
$ fg 1
ping 192.168.10.56 &> ping.log
^Z
[1]+  Stopped                 ping 192.168.10.56 &> ping.log
$ bg 1
[1]+ ping 192.168.10.56 &> ping.log &
$ fg 1
ping 192.168.10.56 &> ping.log
^C

#!/bin/bash -
#!/usr/bin/env bash

# output
echo 'word'
printf 'word\n'

VARNAME=varvaluetext
# to get the var, prepend a $
echo $VARNAME

# single quotes preseve space
VARNAME='this is the variable value'
# double quotes allow substitutions
NEWVAR="this is $VARNAME"

# store value of shell command
PRINTDIR=$(pwd)
echo $PRINTDIR

$@ # stores all args and makes them avaialable in array
$0 # name of script
$1 # first param
$2 # second param
$# # number of params passed
$? # value returned by previous command

for var in $@
do
    echo "Hello, $var."
done

# 'for' loops over the arguments by default, as long as you don't ad the 'in x' part
for ARG
do
    echo here is an argument: $ARG
done

# read accepts input from stdin and stores in var
read INPUTVAR
echo $INPUTVAR

# if a command returns a 0, then do x, y, and z
if <command>
then
    <something>
else
    <something else>
fi

# [[ ]] is the compound command
if [[ -e $FILENAME ]]
then
    echo $FILENAME existsd
fi

# if VAR has a value
if [[ $VAR ]]; then
    # do something
fi

# numbers
if [[ $VAL -lt $MIN ]]
then
    echo "$VAL is too small"
fi

# for arithmetic operations, or when comparing numbers with 
# the < or > signs, use (( ))
if (( VAL > 2))
then
    echo "value $VAL is too small
fi

if (( $? )) ; then echo "previous command failed" ; fi

# while loop
i=0
while (( i < 100 ))
do
    echo $i
    let i++
done

# for loop
for ((i=0; i < 100; i++))
do
    echo $i
done

function myfunc()
{
    # do something
}

# call functions like a shell command
myfunc arg1 arg2 arg3

# both of these functions run in a subshell
myfunc arg1 arg1 | next-step | etc
RETVAL=$(myfunc arg1 arg1)

*   # match any number of any character
?   # match a single character ex. source.? returns source.c but not source.cpp
[ ] # match any of the characters within the brackets

[0-9]  # range
[!cat] # match anything other than the chars in the brackets
[^cat] # match anything other than the chars in the brackets
*[[:punct:]]jpg # match any file with any number of characters followed by a 
                # punctuation character, then 'jpg'

grep <options> <pattern> <filenames>
grep -R -i 'password' /home

# egrep to extend syntax for ?, +, {, |, (, and )

. # match any single character except newline
? # preceding char is optional, match zero or one time
* # preceding char is optional, match zero or more times
+ # match preceding char one or more times

egrep 'And be one (stranger|traveler), long I stood' frost.txt 
3    And be one traveler, long I stood

egrep <([a-zA-Z]*)>.*</\1> file.txt

T{5}   # T must appear 5 consecutive times
T{3,6} # T must appear 3 to 6 times
T{5,}  # T must appear 5 or more times

^[1-5] # beginning anchor. Matching string must start with 1-5 as the first char
[1-5]$ # end anchor. Matching string must end with 1-5 as the first char

# sort by 3rd column
sort -k 3 filename.txt

# sort by chars 4 and 5 of field 2 (non-zero index)
sort -k 2.4,2.5 filename.txt

... | sort -k 2.1 -rn | head -15

# -A is assoc. array for bash 4.0+
declare -A arrayName1 arrayName2

# lowercase a is a regular array
declare -a RA_key RA_val

# access el in array
${ar[index]}

# get key values already in assoc. array (key, val)--don't think
# that the '!' negates a value--it is part of the language
${!ar[@]}

# each variable for read gets assigned the corresponding var
# so, index gets the first word, xtra gets remaining. If there
# are no remaining, xtra is empty string.
while read index xtra
do
    # do stuff
done

for var in "${!array[@]}"
do
    # do something
done

# id is 15 chars long, left-justified (-15)
# %8 is 8 digits long
printf "%-15s %8d\n" "${id}" "{cnt[${id}]}"

# use the i to declare integers (4 here)
local -i i raw maxraw scale

# you don't need $ to indicate 'value of'
((result=(COUNT*i)/maxcount))

ssh <hostname> command
ssh mycomputer ps

# redirect to file on local machine
ssh <hostname> ps > filename.out

# redirect on remote machine
#   backslash escapes > on local shell, passes to 
#   remote where it is executed)
ssh <hostname> ps \> /tmp/ps.out

# run local script on remote system.
#   This runs the bash command on the remote and 
#   passes that command the lines of script.sh
ssh <hostname> bash < ./script.sh

# ${} is parameter expansion, which retrieves the value of a variable
tar -czf ${HOSTNAME}_logs.tar.gz /var/logs

readarray INPUTARRAY

for LINE in "${INPUTARRAY[@]}"; do
    # do work
done

# read contents of file into VAR array. -t removes trailing \n
readarry -t VAR < file.txt

# '#' means match from the left (like comments)
# '%' means match from the right (like 5%, in general math) 

# removes everything to the right of STRING, including "|"
VAR=${STRING%%|*}

# removes first match to left of STRING, including "|"
VAR=${STRING#*|}

# removes SUBSTRING
VAR=${STRING//SUBSTRING/}

# find searchs provided dir and subdir
# name searches for file name that matches pattern
find /home -name '*password*'
find /home -name '.*'

# surpress errors
find /home -name '*password*' 2>/dev/null

# file > 5GB
find /home -size +5G

# find 5 largest files in filesystem, supressing errors
ls / -R -s 2>/dev/null | sort -n -r | head -5

# modified time searches
find /home -mmin -5         # modified less than 5 mins ago
find /home -mtime -1        # modified less than 24 hrs ago
find /home -mtime +2        # modified more than 2 days ago
find /home -atime -1        # modified less than 24 hours ago

# exec option executes the command and replaces '{}' with the filepath
# search for all files in /home that were accessed less than 24 
# hours ago, and copy them to the pwd
find /home -type f -atime -1 -exec cp '{}' ./ \;    # '\;' ends the exec clause, not separate bash commands
                                                    # '{}' expands to the path of each result found in /home

# content search

# search home and subdirs for the string 'password'
grep -r -i /home -e 'password'  # -e means use regex

# find and grep. get all files in /home with password in the title and copy to pwd
find /home -type -f -exec grep 'password' '{}' \; -exec cp '{}' . \;


# search by file type

find $DIR <option> -type f | while read FN; do
    file $FN | egrep -q $CASEMATCH "$PATTERN"
    if (($? == 0)); then # found one
        echo $FN
        if [[ $COPY ]]; then
            cp -p $FN $DESTDIR
        fi
    fi
done

# while loop that uses getops builtin
# 'c:irR' are the accepted options. ":" means "c" accepts an arg
# opt is user-provided variable that shell stores each option
#   in for the loop
# OPTARG is the arg currently in process
# OPTIND is the next arg
while getopts 'c:irR' opt; do
    case "${opt}" in
    c) # copy found files to specified directory
        COPY=YES
        DESTDIR="$OPTARG"
        ;;
    i) # ignore u/l case differences in search
        CASEMATCH='-i'
        ;;
    [Rr]) # recursive, accept upper or lowercase
        unset DEEPORNOT ;;
    *)  # matches anything--unknown/unsupported option
        # error mesg will com from getopts, so just exit
        exit 2 ;;
    esac
done
# shift resets parsed args. If 3 args were read, this resets the arg count of the next arg to be processed(OPTIND) from $4 to $1.
# getops tracks args with OPTIND-it refers to the next arg to be processed
shift $((OPTIND - 1))

# :- means if PATTERN isn't set, set to 'PDF document'
# set STARTDIR to '.'
PATTERN=${1:-PDF document} # use 1st arg, but if not set, use 'PDF document'
STARTDIR=${2:-.} # use the 2nd arg, but if not set, use cwd

$ sha1sum cmd.txt 
a5376365573cea36944c5fafe6793101e096a632  cmd.txt

# can add a similar line to end of collection scripts
scp info.tar.gz user@hostname:/home/path/to/dest

uppercase=$(echo $var | tr '[a-z]' '[A-Z]')

lowercase=$(echo $var | tr '[A-Z]' '[a-z]')

$ typeset -u my_name
$ my_name='Sally'
$ echo $my_name 
SALLY


$ typeset -l last_name
$ last_name='Ride'
$ echo $last_name 
ride