Given a previously defined $LINE in a shell script, I do the following
var1=$(echo $LINE | cut -d, -f4)
var2=$(echo $LINE | cut -d, -f5)
var3=$(echo $LINE | cut -d, -f6)
Is there any way for me to combine it into one command, where the cut is run only once?
Something like
var1,var2,var3=$(echo $LINE | cut -d, -f4,5,6)
The builtin read command can assign to multiple variables:
IFS=, read _ _ _ var1 var2 var3 _ <<< "$LINE"
yes, if you're ok with arrays:
var= ( $(echo $LINE | cut -d, --output-delimiter=' ' -f4-6) )
Note that that make var 0-indexed.
Though it might just be quicker and easier to turn the CSV $LINE into something that bash parenthesis understand, and then just do var = ( $LINE ).
EDIT: The above will cause issues if you have spaces in your $LINE... if so, you need to be a bit more careful, and AWK might be a better choice to add quotes:
var= ( $( echo $LINE | awk IFS=, '{print "\"$4\" \"$5\" \"$6\""}' ) )
Related
I have a text file with a whole bunch of lines (1000 exactly) and they all have 4 bits of text, seperated by a ;.
Here is the for loop I'm using, to go through each line:
while IFS= read -r line; do
let liner++
if [[ liner -eq "1" ]]; then
continue
fi
name=$(echo "${line}" | cut -d';' -f1)
fullname=$(echo "${line}" | cut -d';' -f2)
id=$(echo "${line}" | cut -d';' -f3)
test=$(echo "${line}" | cut -d';' -f4)
echo "${GREEN}$(($liner-1))) ${name} ${ORANGE}v${test} ${RED}(${id})${NC}"
stuff+=("${fullname}")
done < list.txt
It takes about 5 seconds before it finishes running and I believe it's from all those cut (name, fullname, id, test) variables. What would be the best solution to speed this up?
Awk undoubtedly provides a better solution, but if you don't want to learn Awk right now, you could speed your function up a lot by just using read to split the lines into fields:
liner=0
stuff=()
while IFS=\; read -r name fullname id test; do
echo "$GREEN$((++liner))) $name ${ORANGE}v$test $RED($id)$NC"
stuff+=("$fullname")
done < <(tail -n+2 1000num.txt)
I'm trying to print domain and topLeveldomain variables (example.com)
$line = example.com
domain =$line | cut -d. -f 1
topLeveldomain = $line | cut -d. -f 2
However when I try and echo $domain, it doesn't display desired value
test.sh: line 4: domain: command not found
test.sh: line 5: topLeveldomain: command not found
I suggest:
line="example.com"
domain=$(echo "$line" | cut -d. -f 1)
topLeveldomain=$(echo "$line" | cut -d. -f 2)
The right code for this should be:
line="example.com"
domain=$(echo "$line" | cut -d. -f 1)
topLeveldomain=$(echo "$line" | cut -d. -f 2)
Consider the right syntax of bash:
variable=value
(there are no blanks allowed)
if you want to use the content of the variable you have to add a leading $
e.g.
echo $variable
You don't need external tools for this, just do this in bash
$ string="example.com"
# print everything upto first de-limiter '.'
$ printf "${string%%.*}\n"
example
# print everything after first de-limiter '.'
$ printf "${string#*.}\n"
com
Remove spaces around =:
line=example.com # YES
line = example.com # NO
When you create a variable, do not prepend $ to the variable name:
line=example.com # YES
$line=example.com # NO
When using pipes, you need to pass standard output to the next command. Than means, you usually need to echo variables or cat files:
echo $line | cut -d. -f1 # YES
$line | cut -d. -f1 # NO
Use the $() syntax to get the output of a command into a variable:
new_variable=$(echo $line | cut -d. -f1) # YES
new_variable=echo $line | cut -d. -f1 # NO
I would rather use AWK:
domain="abc.def.hij.example.com"
awk -F. '{printf "TLD:%s\n2:%s\n3:%s\n", $NF, $(NF-1), $(NF-2)}' <<< "$domain"
Output
TLD:com
2:example
3:hij
In the command above, -F option specifies the field separator; NF is a built-in variable that keeps the number of input fields.
Issues with Your Code
The issues with your code are due to invalid syntax.
To set a variable in the shell, use
VARNAME="value"
Putting spaces around the equal sign will cause errors. It is a good
habit to quote content strings when assigning values to variables:
this will reduce the chance that you make errors.
Refer to the Bash Guide for Beginners.
this also works:
line="example.com"
domain=$(echo $line | cut -d. -f1)
toplevel=$(cut -d. -f2 <<<$line)
echo "domain name=" $domain
echo "Top Level=" $toplevel
You need to remove $ from line in the beginning, correct the spaces and echo $line in order to pipe the value to cut . Alternatively feed the cut with $line.
Right Now I am trying to parse the values from my get time and date and break it down by each number
Format of the date/time
#!/bin/bash
prevDateTime=$(date +'%Y-%m-%d-%H:%M:%S')
echo "${prevDateTime}"
I want to be able to list it out like so
echo "${prevYear}"
echo "${prevMonth}"
echo "${prevDay}"
echo "${prevHour}"
echo "${prevMinute}"
echo "${prevSecond}"
and then like
echo "${prevDate}"
echo "${precTime}"
But I am not sure how to parse out the information any help would be great
A regular expression is probably the simplest solution, given the format of prevDateTime.
[[ $prevDateTime =~ (.*)-(.*)-(.*)-(.*):(.*):(.*) ]]
prevYear=${BASH_REMATCH[1]}
prevMonth=${BASH_REMATCH[2]}
# etc.
Technically, there's a "one"-liner to do this using declare:
declare $(date +'prevDateTime=%Y-%m-%d:%H:%M:%S
prevYear=%Y
prevMonth=%m
prevDat=%d
prevHour=%H
prevMinute=%M
prevSecond=%S')
It uses date to output a block of parameter assignments which declare instantiates. (Note that the command substitution is not quoted, so that each assignment is seen as a separate argument to declare. If there was any whitespace in the values to assign, you would have to switch to using eval with slightly different output from date.)
You can use read command with IFS to break down date components:
prevDateTime=$(date +'%Y-%m-%d-%H:%M:%S')
IFS='-:' read -ra arr <<< "$prevDateTime"
# print array values
declare -p arr
# This outputs
# declare -a arr='([0]="2015" [1]="05" [2]="21" [3]="10" [4]="24" [5]="28")'
#assign to other variables
prevYear=${arr[0]}
prevMonth=${arr[1]}
prevDay=${arr[2]}
prevHour=${arr[3]}
prevMinute=${arr[4]}
prevSecond=${arr[5]}
Fast solution using cut:
#!/bin/bash
prevDateTime=$(date +'%Y-%m-%d-%H:%M:%S')
echo "${prevDateTime}"
prevYear=`echo $prevDateTime | cut -d- -f1`
prevMonth=`echo $prevDateTime | cut -d- -f2`
prevDay=`echo $prevDateTime | cut -d- -f3`
prevHour=`echo $prevDateTime | cut -d- -f4 | cut -d: -f1`
prevMinute=`echo $prevDateTime | cut -d- -f4 | cut -d: -f2`
prevSecond=`echo $prevDateTime | cut -d- -f4 | cut -d: -f3`
echo "Year: $prevYear; Month: $prevMonth; Day: $prevDay"
echo "Hour: $prevHour; Minute: $prevMinute; Second: $prevSecond"
I have entries of the form: cat:rat and I would like to assign them to separate variables in bash. I am currently able to do this via:
A=$(echo $PAIR | tr ':' '\n' | head -n1)
B=$(echo $PAIR | tr ':' '\n' | tail -n1)
after which $A and $B are, respectively, cat and rat. echo, the two pipes and all feels a bit like overkill am I missing a much simpler way of doing this?
Using the read command
entry=cat:rat
IFS=: read A B <<< "$entry"
echo $A # => cat
echo $B # => rat
Yes using bash parameter substitution
PAIR='cat:rat'
A=${PAIR/:*/}
B=${PAIR/*:/}
echo $A
cat
echo $B
rat
Alternately, if you are willing to use an array in place of individual variables:
IFS=: read -r -a ARR <<<"${PAIR}"
echo ${ARR[0]}
cat
echo ${ARR[1]}
rat
EDIT: Refer glenn jackman's answer for the most elegant read-based solution
animal="cat:rat"
A=echo ${animal} | cut -d ":" -f1
B=echo ${animal} | cut -d ":" -f2
might not be the best solution. Just giving you a possible solution
I have the following:
FILENAME=$1
cat $FILENAME | while read LINE
do
response="$LINE" | cut -c1-14
request="$LINE" | cut -c15-31
difference=($response - $request)/1000
echo "$difference"
done
When I run this script it returns blank lines. What am I doing wrong?
Might be simpler in awk:
awk '{print ($1 - $2)/1000}' "$1"
I'm assuming that the first 14 chars and the next 17 chars are the first two blank-separated fields.
You need to change it to:
response=`echo $LINE | cut -c1-14`
request=`echo $LINE | cut -c15-31`
difference=`expr $response - $request`
val=`expr $difference/1000`
You are basically doing everything wrong ;)
This should be better:
FILENAME="$1"
cat "$FILENAME" | while read LINE
do
response=$(echo "$LINE" | cut -c1-14) # or cut -c1-14 <<< "$line"
request=$(echo "$LINE" | cut -c15-31)
difference=$((($response - $request)/1000)
echo "$difference"
done