Bash for loop skip first element of array - bash

In bash,
I have a string, I want to convert in array and use it in a for loop but skipping the first element. The code below does not works:
build_string="100 99 98"
build_list=("$build_string")
echo $build_list
for i in "${build_list[#]:1}"
do echo "i: " $i
done
The for loop does not print anything. Could you help me? Thanks.

I believe you are not converting the array properly (or at all).
Please see this snippet:
build_string="100 99 98"
#build_list=("$build_string") <-- this is not converting into array, following line is.
IFS=' ' read -r -a build_list <<< "$build_string"
echo $build_list
for i in "${build_list[#]:1}"
do echo "i: " $i
done
sleep 2
now the output is:
100
i: 99
i: 98
Which sounds reasonable. The 100 is printed when you ask echo $build_string.
Reference: split string into array in bash
As pointed out by prefire, the double quotes on the second line are preventing array conversion. This snippet also works:
build_string="100 99 98"
build_list=($build_string)
echo $build_list
for i in "${build_list[#]:1}"
do echo "i: " $i
done
sleep 2
Note: I've added a sleep 2 at the end, so I can see what is being printed.

Replace the second line with this:
build_list=($build_string)

build_list=("$build_string")
build_list array only have one item, so
${build_list[#]:1 is empty.

Related

How to declare array in shell script?

I am trying to declare an array in my shell script and then have written a for loop to access those array elements into another file. But it is only taking the first element. I've tried the below :
raw_cd=(1150 1151)
i=0
for i in "${raw_cd[#]}"
do
grep -wr "${raw_cd[#]}" file1.txt > /opt/tmp/raw.txt
echo "$i"
done
It is taking only the first element 1150 and also giving output as :-
file1.txt:|1150|
file1.txt:|1150|
file1.txt:|1150|
where am i doing wrong?
for does not deal with indices, just raw values. Thus,
raw_cd=(1150 1151)
for i in "${raw_cd[#]}"
do
echo "$i"
done
will print
1150
1151
If you want to use indices, you need to produce them yourself:
raw_cd=(1150 1151)
for i in $(seq "${#raw_cd[#]}")
do
echo "$i": "${raw_cd[$i - 1]}"
done
will produce
1: 1150
2: 1151
Even better, you can directly get keys like this, without seq (this will work even on associative arrays):
raw_cd=(1150 1151)
for i in "${!raw_cd[#]}"
do
echo "$i": "${raw_cd[$i]}"
done

I stored values in Multi Dimensional Array. When printing the values, it's printing the second iteration values and first iteration is being replaced

This block of code is looping through a file and loading each word into a multi dimensional array.
lcv=0
declare -A db
while read line;
do
lcv1=0
echo $line
for i in $line;
do
db[$lcv,$lcv1]=$i
echo $lcv,$lcv1,${db[$lcv,$lcv1]};
#echo ${db[$lcv]}
((++lcv1))
done
((++lcv))
done < data.txt # File Contains records of 4 fields.
echo ${db[0,1]}
echo ${db[0,0]}
Little pseudo 2D array using bash
I just re-use your algorithm, whiping all echo and useless steps.
#!/bin/bash
unset x y db
y=0
declare -A db
while read line ;do
for i in $line ;do
db[$((x++)),$y]=$i
done
((y++))
x=0
done <<<$'0 1 2 3\n4 5 6 7\n8 9 a b\nc d e f'
Now if you
declare -p db x y
bash will print:
declare -A db='([0,0]="0" [0,1]="4" [0,2]="8" [0,3]="c" [3,3]="f" [3,2]="b" [3,1]="7" [3,0]="3" [2,2]="a" [2,3]="e" [2,0]="2" [2,1]="6" [1,1]="5" [1,0]="1" [1,3]="d" [1,2]="9" )'
declare -- x="0"
declare -- y="4"
At this point, I just wanna purpose to change 9th line: ((y++)) by ((y++,maxx=maxx>x?maxx:x)). This will populate maxx (to 4 in this sample)
Then inverting the array:
for i in {0..4};do # this syntax is nice, but don't support variables
for((j=0;j<y;j++)){ # this syntaxe could use variables
echo -n ${db[$i,$j]}\
}
echo
done
will print:
0 4 8 c
1 5 9 d
2 6 a e
3 7 b f
If the data.txt contains this:
$ cat data.txt
l0val0 l0val1 l0val2 l0val3
l1val0 l1val1 l1val2 l1val3
l2val0 l2val1 l2val2 l2val3
l3val0 l3val1 l3val2 l3val3
l4val0 l4val1 l4val2 l4val3
l5val0 l5val1 l5val2 l5val3
Your program produce this:
$ ./script
l0val0 l0val1 l0val2 l0val3
0,0,l0val0
0,1,l0val1
0,2,l0val2
0,3,l0val3
l1val0 l1val1 l1val2 l1val3
1,0,l1val0
1,1,l1val1
1,2,l1val2
1,3,l1val3
l2val0 l2val1 l2val2 l2val3
2,0,l2val0
2,1,l2val1
2,2,l2val2
2,3,l2val3
l3val0 l3val1 l3val2 l3val3
3,0,l3val0
3,1,l3val1
3,2,l3val2
3,3,l3val3
l4val0 l4val1 l4val2 l4val3
4,0,l4val0
4,1,l4val1
4,2,l4val2
4,3,l4val3
l5val0 l5val1 l5val2 l5val3
5,0,l5val0
5,1,l5val1
5,2,l5val2
5,3,l5val3
l0val1
l0val0
That goes to show that the value of $lcv selects each row (line), and the value of $lcv1 selects each word (record) divided on spaces or tabs.
It is working correctly from what I can see.
If we add this lines at the end of the script:
echo "end of first script"
for i in {0..5}; do
for j in {0..3}; do
printf 'db[%s,%s]=%s ' "$i" "$j" "${db[$i,$j]}"
done
echo
done
echo
declare -p db
We will get this output:
end of first script
db[0,0]=l0val0 db[0,1]=l0val1 db[0,2]=l0val2 db[0,3]=l0val3
db[1,0]=l1val0 db[1,1]=l1val1 db[1,2]=l1val2 db[1,3]=l1val3
db[2,0]=l2val0 db[2,1]=l2val1 db[2,2]=l2val2 db[2,3]=l2val3
db[3,0]=l3val0 db[3,1]=l3val1 db[3,2]=l3val2 db[3,3]=l3val3
db[4,0]=l4val0 db[4,1]=l4val1 db[4,2]=l4val2 db[4,3]=l4val3
db[5,0]=l5val0 db[5,1]=l5val1 db[5,2]=l5val2 db[5,3]=l5val3
declare -A db=([1,1]="l1val1" [1,0]="l1val0" [1,3]="l1val3" [1,2]="l1val2" [0,0]="l0val0" [0,1]="l0val1" [0,2]="l0val2" [0,3]="l0val3" [5,1]="l5val1" [5,0]="l5val0" [5,3]="l5val3" [5,2]="l5val2" [3,3]="l3val3" [3,2]="l3val2" [3,1]="l3val1" [3,0]="l3val0" [2,2]="l2val2" [2,3]="l2val3" [2,0]="l2val0" [2,1]="l2val1" [4,0]="l4val0" [4,1]="l4val1" [4,2]="l4val2" [4,3]="l4val3" )
Now, the question is: What do you think that is wrong?.

bash Command line substitution in for loop

I have a test script test.sh where I am trying to print out command line arguments.to the script but the following does not work as expected
`#!/bin/bash
for((i=1;i<"$#";i++)) do
printf "Position %s of argumentArray has %s \n", $i $(($i))
done`
( my idea was that the (()) will do the mathematical evaluation resulting in $1 $2 etc.) Neither does
for((i=1;i<"$#";i++)) do
printf "Position %s of argumentArray has %s \n", $i $"$( eval echo $i )"
done
both gives as out put when run as follows
./test.sh first second third
Position 1 of argumentArray has 1
Position 1 of argumentArray has 2
Position 1 of argumentArray has 3
instead of
Position 1 of argumentArray has first
Position 1 of argumentArray has second
Position 1 of argumentArray has third
I face the same problem with
for((i=1;i<="$#";i++))
do
case "$($i)" in
.......
case evaluates to 1 ,2 3 etc insted of the actual parameter passed in.
Please help me in understanding where I am going wrong.
You can use indirect expansion to do this fairly easily:
for((i=1;i<=$#;i++)) do
printf "Position %s of argumentArray has %s \n" $i "${!i}"
done
I also fixed some minor problems in the above: the loop end condition should be i<=$# to print the last arg, there shouldn't be a comma after the format string for printf, and there should be double-quotes around the argument ("${!i}") in case it has any spaces or other funny characters.
The commandline arguments can be accessed directly but if you want them by position you can do this:
arguments=($#)
for ((i = 0; i < ${#arguments[#]}; i++)); do
echo "arguments[$i] = ${arguments[$i]}"
done
A run of the script:
$ ./args.sh first second third
arguments[0] = first
arguments[1] = second
arguments[2] = third
ADDENDUM
Information on Bash arrays:
Array chapter from the Advanced Bash Scripting Guide
15 Array tutorials

Concatenate output of two commands into one line

I have a very basic shell script here:
for file in Alt_moabit Book_arrival Door_flowers Leaving_laptop
do
for qp in 10 12 15 19 22 25 32 39 45 60
do
for i in 0 1
do
echo "$file\t$qp\t$i" >> psnr.txt
./command > $file-$qp-psnr.txt 2>> psnr.txt
done
done
done
command calculates some PSNR values and writes a detailed summary to a file for each combination of file, qp and i. That's fine.
The 2>> outputs one line of information that I really need. But when executed, I get:
Alt_moabit 10 0
total 47,8221 50,6329 50,1031
Alt_moabit 10 1
total 47,8408 49,9973 49,8197
Alt_moabit 12 0
total 47,0665 50,1457 49,6755
Alt_moabit 12 1
total 47,1193 49,4284 49,3476
What I want, however, is this:
Alt_moabit 10 0 total 47,8221 50,6329 50,1031
Alt_moabit 10 1 total 47,8408 49,9973 49,8197
Alt_moabit 12 0 total 47,0665 50,1457 49,6755
Alt_moabit 12 1 total 47,1193 49,4284 49,3476
How can I achieve that?
(Please feel free to change the title if you think there's a more appropriate one)
You could pass the -n option to your first echo command, so it doesn't output a newline.
As a quick demonstration, this :
echo "test : " ; echo "blah"
will get you :
test :
blah
With a newline between the two outputs.
While this, with a -n for the first echo :
echo -n "test : " ; echo "blah"
will get you the following output :
test : blah
Without any newline between the two output.
The (GNU version of) echo utility has a -n option to omit the trailing newline. Use that on your first echo. You'll probably have to put some space after the first line or before the second for readability.
You can use printf instead of echo, which is better for portability reasons.
printf is the correct way to solve your problem (+1 kurumi), but for completeness, you can also do:
echo "$file\t$qp\t$i $( ./command 2>&1 > $file-$qp-psnr.txt )" >> psnr.txt
While echo -n may work if you just want the print the output to console, it won't work if you want the output redirected to file.
If you want the concatenated output to be redirected to a file, this will work:
echo "Str1: `echo "Str2"`" >> file
I was also facing the same problem.
To define my problem, I have a script which is using the echo function like this:
echo -n "Some text here"
echo -n "Some text here"
The output I was getting is like this:
-n Some text here
-n Some text here
and I want the text to be in same line and it is also printing -n option in the output.
Note :- According to man Page, -n option do not print the trailing newline character.
The way I solved it using by adding the shebang in the starting of the script file like this.
#!/bin/bash
echo -n "Some text here"
echo -n "Some text here"
This will print the desired output like this:
Some text here Some text here
Hope this helps!

How can I shift digits in bash?

I have a homework assignment that is asking to shift a decimal number by a specified amount of digits. More clearly this bash script will take two input arguments, the first is the number(maximum 9 digits) that the shift will be performed on and the second is the number(-9 to 9) of digits to shift. Another requirement is that when a digit is shifted off the end, it should be attached to the other end of the number. One headache of a requirement is that we cannot use control statements of any kind: no loops, no if, and switch cases.
Example: 12345 3 should come out to 345000012 and 12345 -3 should be 12345000
I know that if I mod 12345 by 10^3 I get 345 and then if I divide 12345 by 10^3 I get 12 and then I can just concatenate those two variables together to get 34512. I am not quite sure if that is exactly correct but that is the closest I can get as of now. As far as the -3 shift, I know that 10^-3 is .001 and would work however when I try using 10^-3 in bash I get an error.
I am just lost at this point, any tips would be greatly appreciated.
EDIT: After several hours of bashing (pun intended) my head against this problem, I finally came up with a script that for the most part works. I would post the code right now but I fear another student hopelessly lost might stumble upon it. I will check back and post what I came up with in a week or two. I was able to do it with mods and division. Thank you all for the responses, it really helped me to open up and think about the problem from different angles.
Here's a hint:
echo ${string:0:3}
echo ${#string}
Edit (2011-02-11):
Here's my solution. I added some additional parameters with defaults.
rotate-string ()
{
local s=${1:-1} p=${2:--1} w=${3:-8} c=${4:-0} r l
printf -vr '%0*d' $w 0 # save $w zeros in $r
r=${r//0/$c}$s # change the zeros to the character in $c, append the string
r=${r: -w} # save the last $w characters of $r
l=${r: -p%w} # get the last part of $r ($p mod %w characters)
echo "$l${r::w-${#l}}" # output the Last part on the Left and the Right part which starts at the beginning and goes for ($w minus the_length_of_the_Left_part) characters
}
usage: rotate-string string positions-to-rotate width fill-character
example: rotate-string abc -4 9 =
result: ==abc====
Arguments can be omitted starting from the end and these defaults will be used:
fill-character: "0"
width: 8
positions-to-rotate: -1
string: "1"
More examples:
$ rotate-string
00000010
$ rotate-string 123 4
01230000
Fun stuff:
$ for i in {126..6}; do printf '%s\r' "$(rotate-string Dennis $i 20 .)"; sleep .05; done; printf '\n'
$ while true; do for i in {10..1} {1..10}; do printf '%s\r' "$(rotate-string : $i 10 .)"; sleep .1; done; done
$ while true; do for i in {40..2} {2..40}; do printf '%s\r' "$(rotate-string '/\' $i 40 '_')"; sleep .02; done; done
$ d=0; while true; do for i in {1..10} {10..1}; do printf '%s\r' "$(rotate-string $d $i 10 '_')"; sleep .02; done; ((d=++d%10)); done
$ d=0; while true; do for i in {1..10}; do printf '%s\r' "$(rotate-string $d $i 10 '_')"; sleep .2; ((d=++d%10)); done; done
$ shape='▁▂▃▄▅▆▇█▇▆▅▄▃▂▁'; while true; do for ((i=1; i<=COLUMNS; i++)); do printf '%s\r' "$(rotate-string "$shape" $i $COLUMNS ' ')"; done; done
In the absence of control structures, you need to use recursion, with index values as "choice selections", which is how functional programming often works.
#!/bin/sh
#
# cshift NUMBER N
cshift() {
let num=10#$1
num=`printf '%09d' $num`
lshift="${num:1:8}${num:0:1}"
rshift="${num:8:1}${num:0:8}"
next=( "cshift $lshift $(($2 + 1))" "echo $num" "cshift $rshift $(( $2 - 1 ))" )
x=$(( $2 == 0 ? 1 : $2 < 0 ? 0 : 2 ))
eval "${next[x]}"
}
cshift $1 $2
and, the testing:
$ for ((i=-9;i<=9;i++)); do cshift 12345 $i ; done
000012345
500001234
450000123
345000012
234500001
123450000
012345000
001234500
000123450
000012345
500001234
450000123
345000012
234500001
123450000
012345000
001234500
000123450
000012345
You can also do some math on the indexes and avoid the recursion, but I don't mind making the computer work harder so I don't have to. It's easy to think of how to do the shift by one in either direction, and then I use an evaluated choice that is selected by the signum of the shift value, outputting a value and stopping when the shift value is zero.

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