I have to write a script, which will take all arguments and print them in reverse.
I've made a solution, but find it very bad. Do you have a smarter idea?
#!/bin/sh
> tekst.txt
for i in $*
do
echo $i | cat - tekst.txt > temp && mv temp tekst.txt
done
cat tekst.txt
Could do this
for (( i=$#;i>0;i-- ));do
echo "${!i}"
done
This uses the below
c style for loop
Parameter indirect expansion
(${!i}towards the bottom of the page)
And $# which is the number of arguments to the script
you can use this one liner:
echo $# | tr ' ' '\n' | tac | tr '\n' ' '
bash:
#!/bin/bash
for i in "$#"; do
echo "$i"
done | tac
call this script like:
./reverse 1 2 3 4
it will print:
4
3
2
1
Portably and POSIXly, without arrays and working with spaces and newlines:
Reverse the positional parameters:
flag=''; c=1; for a in "$#"; do set -- "$a" ${flag-"$#"}; unset flag; done
Print them:
printf '<%s>' "$#"; echo
Reversing a simple string, by spaces
Simply:
#!/bin/sh
o=
for i;do
o="$i $o"
done
echo "$o"
will work as
./rev.sh 1 2 3 4
4 3 2 1
Or
./rev.sh world! Hello
Hello world!
If you need to output one line by argument
Just replace echo by printf "%s\n":
#!/bin/sh
o=
for i;do
o="$i $o"
done
printf "%s\n" $o
Reversing an array of strings
If your argument could contain spaces, you could use bash arrays:
#!/bin/bash
declare -a o=()
for i;do
o=("$i" "${o[#]}")
done
printf "%s\n" "${o[#]}"
Sample:
./rev.sh "Hello world" print will this
this
will
print
Hello world
As a function (If you're ok to play with eval.
But eval is evil!!
rev() { eval "set --" $(seq -f '"${%g}"' $# -1 1);printf '%s\n' "$#";}
Then
rev Hello\ world print will this
this
will
print
Hello world
Related
I am new to bash and I struggling with a program. I want to write a program that first asks for user input and afterwards prints the words with an \n(blank line) between them. The last echo contains the amount of characters that is written. Also the output can only contain the words and no digits. E.g:
Input: hallo1 user2 Pete4
Ouput: hallo
user
Pete
13 Characters
This is my code for the time beeing.
echo Typ one or multiple words:
read varname
arr=( "${arr[#]}" "$varname" )
for i in "${arr[#]}"; do
echo "$i"
done
echo ${arr[#]}
# printf '%s\n' "${arr[#]}"
Try this. Works for me. I added in the for the sentence to remove the digits.
And after the for, I first remove the spaces between the names and then I count the total of characters using the # in ${#aux}. I added the parameter -n in the first echo too, just to break the line with the second one.
echo Type one or multiple words:
read varname
arr=( "${arr[#]}" "$varname" )
for i in "${arr[#]//[[:digit:]]/}"; do
echo -n "$i"
done
aux=$(echo "${i}" | sed "s/ //g")
echo " " ${#aux} " Characters"
An approach in plain bash without using an array:
#!/bin/bash
echo 'Type one or multiple words on a line:'
read -r
words_without_digits=${REPLY//[0-9]}
line_without_blanks=${words_without_digits//[[:blank:]]}
printf '%s\n' $words_without_digits
echo "${#line_without_blanks} Characters"
echo Type one or multiple words:
read varname
arr=( "${arr[#]}" "$varname" )
for i in "${arr[#]//[[:digit:]]/}"; do
printf '%s\n' $i
done
aux=$(echo "${i}" | sed "s/ //g")
echo ${#aux} " Characters"
I have a file with lines. I want to reverse the words, but keep them in same order.
For example: "Test this word"
Result: "tseT siht drow"
I'm using MAC, so awk doesn't seem to work.
What I got for now
input=FILE_PATH
while IFS= read -r line || [[ -n $line ]]
do
echo $line | rev
done < "$input"
Here is a solution that completely avoids awk
#!/bin/bash
input=./data
while read -r line ; do
for word in $line ; do
output=`echo $word | rev`
printf "%s " $output
done
printf "\n"
done < "$input"
In case xargs works on mac:
echo "Test this word" | xargs -n 1 | rev | xargs
Inside your read loop, you can just iterate over the words of your string and pass them to rev
line="Test this word"
for word in "$line"; do
echo -n " $word" | rev
done
echo # Add final newline
output
tseT siht drow
You are actually in fairly good shape with bash. You can use string-indexes and string-length and C-style for loops to loop over the characters in each word building a reversed string to output. You can control formatting in a number of ways to handle spaces between words, but a simple flag first=1 is about as easy as anything else. You can do the following with your read,
#!/bin/bash
while read -r line || [[ -n $line ]]; do ## read line
first=1 ## flag to control space
a=( $( echo $line ) ) ## put line in array
for i in "${a[#]}"; do ## for each word
tmp= ## clear temp
len=${#i} ## get length
for ((j = 0; j < len; j++)); do ## loop length times
tmp="${tmp}${i:$((len-j-1)):1}" ## add char len - j to tmp
done
if [ "$first" -eq '1' ]; then ## if first word
printf "$tmp"; first=0; ## output w/o space
else
printf " $tmp" ## output w/space
fi
done
echo "" ## output newline
done
Example Input
$ cat dat/lines2rev.txt
my dog has fleas
the cat has none
Example Use/Output
$ bash revlines.sh <dat/lines2rev.txt
ym god sah saelf
eht tac sah enon
Look things over and let me know if you have questions.
Using rev and awk
Consider this as the sample input file:
$ cat file
Test this word
Keep the order
Try:
$ rev <file | awk '{for (i=NF; i>=2; i--) printf "%s%s",$i,OFS; print $1}'
tseT siht drow
peeK eht redro
(This uses awk but, because it uses no advanced awk features, it should work on MacOS.)
Using in a script
If you need to put the above in a script, then create a file like:
$ cat script
#!/bin/bash
input="/Users/Anastasiia/Desktop/Tasks/test.txt"
rev <"$input" | awk '{for (i=NF; i>=2; i--) printf "%s%s",$i,OFS; print $1}'
And, run the file:
$ bash script
tseT siht drow
peeK eht redro
Using bash
while read -a arr
do
x=" "
for ((i=0; i<${#arr}; i++))
do
((i == ${#arr}-1)) && x=$'\n'
printf "%s%s" $(rev <<<"${arr[i]}") "$x"
done
done <file
Applying the above to our same test file:
$ while read -a arr; do x=" "; for ((i=0; i<${#arr}; i++)); do ((i == ${#arr}-1)) && x=$'\n'; printf "%s%s" $(rev <<<"${arr[i]}") "$x"; done; done <file
tseT siht drow
peeK eht redro
In A.csv, there are
1
2
3
4
How should I read this file and create variables $B and $C so that:
echo $B
echo $C
returns:
1 2 3 4
1,2,3,4
So far I am trying:
cat A.csv | while read A;
do
echo $A
done
It only returns
1
2
3
4
Assuming bash 4.x, the following is efficient, robust, and native:
# Read each line of A.csv into a separate element of the array lines
readarray -t lines <A.csv
# Generate a string B with a comma after each item in the array
printf -v B '%s,' "${lines[#]}"
# Prune the last comma from that string
B=${B%,}
# Generate a string C with a space after each item in the array
printf -v B '%s ' "${lines[#]}"
As #Cyrus said
B=$(cat A.csv)
echo $B
Will output:
1 2 3 4
Because bash will not carry the newlines if the variable is not wrapped in quotes. This is dangerous if A.csv contains any characters which might be affected by bash glob expansion, but should be fine if you are just reading simple strings.
If you are reading simple strings with no spaces in any of the elements, you can also get your desired result for $C by using:
echo $B | tr ' ' ','
This will output:
1,2,3,4
If lines in A.csv may contain bash special characters or spaces then we return to the loop.
For why I've formatted the file reading loop as I have, refer to: Looping through the content of a file in Bash?
B=''
C=''
while read -u 7 curr_line; do
if [ "$B$C" == "" ]; then
B="$curr_line"
C="$curr_line"
else
B="$B $curr_line"
C="$C,$curr_line"
fi
done 7<A.csv
echo "$B"
echo "$C"
Will construct the two variables as you desire using a loop through the file contents and should prevent against unwanted globbing and splitting.
B=$(cat A.csv)
echo $B
Output:
1 2 3 4
With quotes:
echo "$B"
Output:
1
2
3
4
I would read the file into a bash array:
mapfile -t array < A.csv
Then, with various join characters
b="${array[*]}" # space is the default
echo "$b"
c=$( IFS=","; echo "${array[*]}" )
echo "$c"
Or, you can use paste to join all the lines with a specified separator:
b=$( paste -d" " -s < A.csv )
c=$( paste -d"," -s < A.csv )
Try this :
cat A.csv | while read A;
do
printf "$A"
done
Regards!
Try This(Simpler One):
b=$(tr '\n' ' ' < file)
c=$(tr '\n' ',' < file)
You don't have to read File for that. Make sure you ran dos2unix file command. If you are running in windows(to remove \r).
Note: It will modify the file. So, make sure you copied from original file.
This is what i have done to perform this function but I am not getting what i want.
#!/bin/sh
DIRECTIONPART1=4-7-9
for (( i=1; i<=3; i++ ))
do
x=`echo $DIRECTIONPART1| awk -F'-' '{print $i}'`
myarray[$i]=$x
done
for (( c=1; c<=3; c++ ))
do
echo ${myarray[$c]}
done
Problem we realised at this step
x=`echo $DIRECTIONPART1| awk -F'-' '{print $i}'`
Please help me in getting the result
This is what i get :
4-7-9
4-7-9
4-7-9
But I want this:
4
7
9
you are right with line of problem. The problem is that you cant use $i as variable in print. I have tried little workaround which worked for me:
x=`echo $DIRECTIONPART1| awk -F '-' -v var=$i '{print $var }'`
in all it looks like:
#!/bin/sh
DIRECTIONPART1=4-7-9
for (( i=1; i<=3; i++ ))
do
x=`echo $DIRECTIONPART1| awk -F '-' -v var=$i '{print $var }'`
myarray[$i]=$x
done
for (( c=1; c<=3; c++ ))
do
echo ${myarray[$c]}
done
with expected output:
# sh test.sh
4
7
9
#
The simplest portable way to get the desired output is to use $IFS (in a subshell):
#!/bin/sh
DIRECTIONPART1=4-7-9
(IFS=- && echo $DIRECTIONPART1)
The shell array would not work portably, as POSIX, ksh, and bash do not
agree on arrays. POSIX doesn't have any; ksh and bash use different syntax.
If you really want an array, I would suggest to do the entire thing in awk:
#!/bin/sh
DIRECTIONPART1=4-7-9
awk -v v=${DIRECTIONPART1} 'BEGIN {
n=split(v,a,"-")
for (i=1;i<=n;i++) {
print a[i]
}
}'
This will produce one line for each value in the string:
4
7
9
And if you want bash arrays, drop the #!/bin/sh, and do something like this:
#!/bin/bash
DIRECTIONPART1=4-7-9
A=( $(IFS=- && echo $DIRECTIONPART1) )
for ((i=0;i<=${#A[#]};i++))
do
echo ${A[i]}
done
Calling awk multiple times, or even once, is not the right thing to do. Use the bash built-in read to populate the array.
# Note that the quotes here are only necessary to
# work around a bug that was fixed in bash 4.3. It
# doesn't hurt to use them in any version, though.
$ IFS=- read -a myarray <<< "$DIRECTIONPART_1"
$ printf '%s\n' "${myarray[#]}"
4
7
9
[akshay#localhost tmp]$ bash test.sh
#!/usr/bin/env bash
DIRECTIONPART1=4-7-9
# Create array
IFS='-' read -a array <<< "$DIRECTIONPART1"
#To access an individual element:
echo "${array[0]}"
#To iterate over the elements:
for element in "${array[#]}"
do
echo "$element"
done
#To get both the index and the value:
for index in "${!array[#]}"
do
echo "$index ${array[index]}"
done
Output
[akshay#localhost tmp]$ bash test.sh
4
4
7
9
0 4
1 7
2 9
OR
[akshay#localhost tmp]$ cat test1.sh
#!/usr/bin/env bash
DIRECTIONPART1=4-7-9
array=(${DIRECTIONPART1//-/ })
for index in "${!array[#]}"
do
echo "$index ${array[index]}"
done
Output
[akshay#localhost tmp]$ bash test1.sh
0 4
1 7
2 9
I have in a bash script:
for i in `seq 1 10`
do
read AA BB CC <<< $(cat file1 | grep DATA)
echo ${i}
echo ${CC}
SORT=${CC}${i}
echo ${SORT}
done
so "i" is a integer, and CC is a string like "TODAY"
I would like to get then in SORT, "TODAY1", etc
But I get "1ODAY", "2ODAY" and so
Where is the error?
Thanks
You should try
SORT="${CC}${i}"
Make sure your file does not contain "\r" that would end just in the end of $CC.
This could well explain why you get "1ODAY".
Try including
|tr '\r' ''
after the cat command
try
for i in {1..10}
do
while read -r line
do
case "$line" in
*DATA* )
set -- $line
CC=$3
SORT=${CC}${i}
echo ${SORT}
esac
done <"file1"
done
Otherwise, show an example of file1 and your desired output
ghostdog is right: with the -r option, read avoids succumbing to potential horrors, like CRLFs. Using arrays makes the -r option more pleasant:
for i in `seq 1 10`
do
read -ra line <<< $(cat file1 | grep DATA)
CC="${line[3]}"
echo ${i}
echo ${CC}
SORT=${CC}${i}
echo ${SORT}
done