Think of strings, such as:
I have two apples
He has 4 apples
They have 10 pizzas
I would like to substitute every digit number I find with in a string with a different value, calculated with an external script. In my case, the python program digit_to_word.py convert a digit number to the alphabetic format, but anything will be ok so that I can get the process.
Expected output:
I have two apples
He has four apples
They have ten pizzas
Conceptually:
echo "He has four apples" |
while read word;
do
if [[ "$word" == +([0-9+]) ]]; then
NUM='${python digit_to_word.py "$word"}'
$word="$NUM"
fi
done |
other_operation... | etc..
I say conceptually because I did not get even close to make it work. It is hard to me to even find information on the issue, simply because I do not exactly know how to conceptualize it. At this point, I am mostly reasoning on process substitution, but I am afraid it is not the best way.
Any hint that could be really useful. Thanks in advance for sharing your knowledge with me!
regex='([[:space:]])([0-9]+)([[:space:]])'
echo "He has 4 apples" |
while IFS= read -r line; do
line=" ${line} " # pad with space so first and last words work consistently
while [[ $line =~ $regex ]]; do # loop while at least one replacement is pending
pre_space=${BASH_REMATCH[1]} # whitespace before the word, if any
word=${BASH_REMATCH[2]} # actual word to replace
post_space=${BASH_REMATCH[3]} # whitespace after the word, if any
replace=$(python digit_to_word.py "$word") # new word to use
in=${pre_space}${word}${post_space} # old word padded with whitespace
out=${pre_space}${replace}${post_space} # new word padded with whitespace
line=${line//$in/$out} # replace old w/ new, keeping whitespace
done
line=${line#' '}; line=${line%' '} # remove the padding we added earlier
printf '%s\n' "$line" # write the output line
done
This is careful to work even in some tricky corner cases:
4 score and 14 years ago only replaces the 4 in 4 score with four, and doesn't also modify the 4 in 14.
Input that mixes tabs and whitespaces generates output with the same kinds of whitespace; printf '1\t2 3\n' as your input, and you'll get a tab between one and two, but a space between two and three.
See this running at https://ideone.com/SOsuAD
I'd suggest this is a better job for perl.
To recreate the scenario:
$ cat digit_to_word.sh
case $1 in
4) echo four;;
8) echo eight;;
10) echo ten;;
*) echo "$1";;
esac
$ bash digit_to_word.sh 10
ten
Then this
perl -pe 's/(\d+)/ chomp($word = qx{bash digit_to_word.sh $1}); $word /ge' <<END
I have two apples
He has 4 apples
They have 10 pizzas but only 8 cookies
END
outputs
I have two apples
He has four apples
They have ten pizzas but only eight cookies
However, you've already got some python, why don't you implement the replacement part in python too?
Revision
This approach decomposes each line into two arrays - one for the words and one for the whitespace. Each line is then reconstructed by interleaving the array elements, with digits translated to words by the Python script. Thanks to #Charles Duffy for pointing out some common Bash pitfalls with my original answer.
while IFS= read -r line; do
# Decompose the line into an array of words delimited by whitespace
IFS=" " read -ra word_array <<< $(echo "$line" | sed 's/[[:space:]]/ /g')
# Invert the decomposition, creating an array of whitespace delimited by words
IFS="w" read -ra wspace_array <<< $(echo "$line" | sed 's/\S/w/g' | tr -s 'w')
# Interleave the array elements in the output, translating digits to text
for ((i=0; i<${#wspace_array[#]}; i++))
do
printf "%s" "${wspace_array[$i]}"
if [[ "${word_array[$i]}" =~ ^[0-9]+$ ]]; then
printf "%s" "$(digit_to_word.py ${word_array[$i]})"
else
printf "%s" "${word_array[$i]}"
fi
done
printf "\n"
done < sample.txt
You could use sed for this. Here's an example:
$ echo "He has 4 apples" | sed 's/4/four/'
He has four apples
Looking at the example data though, sed might not be a good fit. If you see "1", you want to replace with "one", but your example replaced "10" with "ten". Do you need to support multi-digit numbers, such as replacing "230" with "two hundred and thirty"?
Related
This question already has answers here:
Extract substring in Bash
(26 answers)
Closed 5 months ago.
I have multiple s3 buckets in AWS whose names are in the following syntax:
resource-4511-deployment-1srsi6fjy9uuk
web-4533-logbucket-dogx6k0n8967
pcnfile6511
5399-bucket-6dehb5uuiwd
I'd like to extract the 4 digit number from each of these names preferably without using multiple if else loops which is the solution I can think of right now. The output should basically be
4511
4533
6511
5399
You can use parameter expansion. Prefix and suffix removal return the strings before and after the four digits, you can then use the removal again to remove the prefix and suffix:
#!/bin/bash
for name in resource-4511-deployment-1srsi6fjy9uuk \
web-4533-logbucket-dogx6k0n8967 \
pcnfile6511 \
5399-bucket-6dehb5uuiwd
do
after=${name#*[0-9][0-9][0-9][0-9]}
before=${name%%[0-9][0-9][0-9][0-9]*}
num=${name#$before}
num=${num%$after}
echo $num
done
I'd use regex matching here.
I was hoping the pattern would be cleaner, but the data forces this:
re='(^|[^[:digit:]])([[:digit:]]{4})($|[^[:digit:]])'
start of string or a non-digit
followed by 4 digits
followed by end of string or a non-digit
for name in resource-4511-deployment-1srsi6fjy9uuk \
web-4533-logbucket-dogx6k0n8967 \
pcnfile6511 \
5399-bucket-6dehb5uuiwd
do
[[ $name =~ $re ]] && echo ${BASH_REMATCH[2]}
done
Assuming there's only one set of 4-digits in each string, one bash idea using a regex and the BASH_REMATCH[] array:
regex='([0-9]{4})'
for string in resource-4511-deployment-1srsi6fjy9uuk web-4533-logbucket-dogx6k0n8967 pcnfile6511 5399-bucket-6dehb5uuiwd
do
[[ "${string}" =~ $regex ]] && echo "${BASH_REMATCH[1]}"
done
This generates:
4511
4533
6511
5399
printf "pcnfile6511" | grep "[0-9][0-9][0-9][0-9]"
That seems to work, although it only will for four digit numbers.
Also...
printf "resource-4511-deployment-1srsi6fjy9uuk" | cut -d'-' -f2
That will work when you have delimiters.
For numbers at the end of a line...
printf "pcnfile6511" | tail -c 4
And for numbers at the beginning...
printf "5399-bucket-6dehb5uuiwd" | head -c 4
I have a string in a Bash shell script that I want to split into an array of characters, not based on a delimiter but just one character per array index. How can I do this? Ideally it would not use any external programs. Let me rephrase that. My goal is portability, so things like sed that are likely to be on any POSIX compatible system are fine.
Try
echo "abcdefg" | fold -w1
Edit: Added a more elegant solution suggested in comments.
echo "abcdefg" | grep -o .
You can access each letter individually already without an array conversion:
$ foo="bar"
$ echo ${foo:0:1}
b
$ echo ${foo:1:1}
a
$ echo ${foo:2:1}
r
If that's not enough, you could use something like this:
$ bar=($(echo $foo|sed 's/\(.\)/\1 /g'))
$ echo ${bar[1]}
a
If you can't even use sed or something like that, you can use the first technique above combined with a while loop using the original string's length (${#foo}) to build the array.
Warning: the code below does not work if the string contains whitespace. I think Vaughn Cato's answer has a better chance at surviving with special chars.
thing=($(i=0; while [ $i -lt ${#foo} ] ; do echo ${foo:$i:1} ; i=$((i+1)) ; done))
As an alternative to iterating over 0 .. ${#string}-1 with a for/while loop, there are two other ways I can think of to do this with only bash: using =~ and using printf. (There's a third possibility using eval and a {..} sequence expression, but this lacks clarity.)
With the correct environment and NLS enabled in bash these will work with non-ASCII as hoped, removing potential sources of failure with older system tools such as sed, if that's a concern. These will work from bash-3.0 (released 2005).
Using =~ and regular expressions, converting a string to an array in a single expression:
string="wonkabars"
[[ "$string" =~ ${string//?/(.)} ]] # splits into array
printf "%s\n" "${BASH_REMATCH[#]:1}" # loop free: reuse fmtstr
declare -a arr=( "${BASH_REMATCH[#]:1}" ) # copy array for later
The way this works is to perform an expansion of string which substitutes each single character for (.), then match this generated regular expression with grouping to capture each individual character into BASH_REMATCH[]. Index 0 is set to the entire string, since that special array is read-only you cannot remove it, note the :1 when the array is expanded to skip over index 0, if needed.
Some quick testing for non-trivial strings (>64 chars) shows this method is substantially faster than one using bash string and array operations.
The above will work with strings containing newlines, =~ supports POSIX ERE where . matches anything except NUL by default, i.e. the regex is compiled without REG_NEWLINE. (The behaviour of POSIX text processing utilities is allowed to be different by default in this respect, and usually is.)
Second option, using printf:
string="wonkabars"
ii=0
while printf "%s%n" "${string:ii++:1}" xx; do
((xx)) && printf "\n" || break
done
This loop increments index ii to print one character at a time, and breaks out when there are no characters left. This would be even simpler if the bash printf returned the number of character printed (as in C) rather than an error status, instead the number of characters printed is captured in xx using %n. (This works at least back as far as bash-2.05b.)
With bash-3.1 and printf -v var you have slightly more flexibility, and can avoid falling off the end of the string should you be doing something other than printing the characters, e.g. to create an array:
declare -a arr
ii=0
while printf -v cc "%s%n" "${string:(ii++):1}" xx; do
((xx)) && arr+=("$cc") || break
done
If your string is stored in variable x, this produces an array y with the individual characters:
i=0
while [ $i -lt ${#x} ]; do y[$i]=${x:$i:1}; i=$((i+1));done
The most simple, complete and elegant solution:
$ read -a ARRAY <<< $(echo "abcdefg" | sed 's/./& /g')
and test
$ echo ${ARRAY[0]}
a
$ echo ${ARRAY[1]}
b
Explanation: read -a reads the stdin as an array and assigns it to the variable ARRAY treating spaces as delimiter for each array item.
The evaluation of echoing the string to sed just add needed spaces between each character.
We are using Here String (<<<) to feed the stdin of the read command.
I have found that the following works the best:
array=( `echo string | grep -o . ` )
(note the backticks)
then if you do: echo ${array[#]} ,
you get: s t r i n g
or: echo ${array[2]} ,
you get: r
Pure Bash solution with no loop:
#!/usr/bin/env bash
str='The quick brown fox jumps over a lazy dog.'
# Need extglob for the replacement pattern
shopt -s extglob
# Split string characters into array (skip first record)
# Character 037 is the octal representation of ASCII Record Separator
# so it can capture all other characters in the string, including spaces.
IFS= mapfile -s1 -t -d $'\37' array <<<"${str//?()/$'\37'}"
# Strip out captured trailing newline of here-string in last record
array[-1]="${array[-1]%?}"
# Debug print array
declare -p array
string=hello123
for i in $(seq 0 ${#string})
do array[$i]=${string:$i:1}
done
echo "zero element of array is [${array[0]}]"
echo "entire array is [${array[#]}]"
The zero element of array is [h]. The entire array is [h e l l o 1 2 3 ].
Yet another on :), the stated question simply says 'Split string into character array' and don't say much about the state of the receiving array, and don't say much about special chars like and control chars.
My assumption is that if I want to split a string into an array of chars I want the receiving array containing just that string and no left over from previous runs, yet preserve any special chars.
For instance the proposed solution family like
for (( i=0 ; i < ${#x} ; i++ )); do y[i]=${x:i:1}; done
Have left overs in the target array.
$ y=(1 2 3 4 5 6 7 8)
$ x=abc
$ for (( i=0 ; i < ${#x} ; i++ )); do y[i]=${x:i:1}; done
$ printf '%s ' "${y[#]}"
a b c 4 5 6 7 8
Beside writing the long line each time we want to split a problem, so why not hide all this into a function we can keep is a package source file, with a API like
s2a "Long string" ArrayName
I got this one that seems to do the job.
$ s2a()
> { [ "$2" ] && typeset -n __=$2 && unset $2;
> [ "$1" ] && __+=("${1:0:1}") && s2a "${1:1}"
> }
$ a=(1 2 3 4 5 6 7 8 9 0) ; printf '%s ' "${a[#]}"
1 2 3 4 5 6 7 8 9 0
$ s2a "Split It" a ; printf '%s ' "${a[#]}"
S p l i t I t
If the text can contain spaces:
eval a=( $(echo "this is a test" | sed "s/\(.\)/'\1' /g") )
$ echo hello | awk NF=NF FS=
h e l l o
Or
$ echo hello | awk '$0=RT' RS=[[:alnum:]]
h
e
l
l
o
I know this is a "bash" question, but please let me show you the perfect solution in zsh, a shell very popular these days:
string='this is a string'
string_array=(${(s::)string}) #Parameter expansion. And that's it!
print ${(t)string_array} -> type array
print $#string_array -> 16 items
This is an old post/thread but with a new feature of bash v5.2+ using the shell option patsub_replacement and the =~ operator for regex. More or less same with #mr.spuratic post/answer.
str='There can be only one, the Highlander.'
regexp="${str//?/(&)}"
[[ "$str" =~ $regexp ]] &&
printf '%s\n' "${BASH_REMATCH[#]:1}"
Or by just: (which includes the whole string at index 0)
declare -p BASH_REMATCH
If that is not desired, one can remove the value of the first index (index 0), with
unset -v 'BASH_REMATCH[0]'
instead of using printf or echo to print the value of the array BASH_REMATCH
One can check/see the value of the variable "$regexp" with either
declare -p regexp
Output
declare -- regexp="(T)(h)(e)(r)(e)( )(c)(a)(n)( )(b)(e)( )(o)(n)(l)(y)( )(o)(n)(e)(,)( )(t)(h)(e)( )(H)(i)(g)(h)(l)(a)(n)(d)(e)(r)(.)"
or
echo "$regexp"
Using it in a script, one might want to test if the shopt is enabled or not, although the manual says it is on/enabled by default.
Something like.
if ! shopt -q patsub_replacement; then
shopt -s patsub_replacement
fi
But yeah, check the bash version too! If you're not sure which version of bash is in use.
if ! ((BASH_VERSINFO[0] >= 5 && BASH_VERSINFO[1] >= 2)); then
printf 'No dice! bash version 5.2+ is required!\n' >&2
exit 1
fi
Space can be excluded from regexp variable, change it from
regexp="${str//?/(&)}"
To
regexp="${str//[! ]/(&)}"
and the output is:
declare -- regexp="(T)(h)(e)(r)(e) (c)(a)(n) (b)(e) (o)(n)(l)(y) (o)(n)(e) (t)(h)(e) (H)(i)(g)(h)(l)(a)(n)(d)(e)(r)(.)"
Maybe not as efficient as the other post/answer but it is still a solution/option.
If you want to store this in an array, you can do this:
string=foo
unset chars
declare -a chars
while read -N 1
do
chars[${#chars[#]}]="$REPLY"
done <<<"$string"x
unset chars[$((${#chars[#]} - 1))]
unset chars[$((${#chars[#]} - 1))]
echo "Array: ${chars[#]}"
Array: f o o
echo "Array length: ${#chars[#]}"
Array length: 3
The final x is necessary to handle the fact that a newline is appended after $string if it doesn't contain one.
If you want to use NUL-separated characters, you can try this:
echo -n "$string" | while read -N 1
do
printf %s "$REPLY"
printf '\0'
done
AWK is quite convenient:
a='123'; echo $a | awk 'BEGIN{FS="";OFS=" "} {print $1,$2,$3}'
where FS and OFS is delimiter for read-in and print-out
For those who landed here searching how to do this in fish:
We can use the builtin string command (since v2.3.0) for string manipulation.
↪ string split '' abc
a
b
c
The output is a list, so array operations will work.
↪ for c in (string split '' abc)
echo char is $c
end
char is a
char is b
char is c
Here's a more complex example iterating over the string with an index.
↪ set --local chars (string split '' abc)
for i in (seq (count $chars))
echo $i: $chars[$i]
end
1: a
2: b
3: c
zsh solution: To put the scalar string variable into arr, which will be an array:
arr=(${(ps::)string})
If you also need support for strings with newlines, you can do:
str2arr(){ local string="$1"; mapfile -d $'\0' Chars < <(for i in $(seq 0 $((${#string}-1))); do printf '%s\u0000' "${string:$i:1}"; done); printf '%s' "(${Chars[*]#Q})" ;}
string=$(printf '%b' "apa\nbepa")
declare -a MyString=$(str2arr "$string")
declare -p MyString
# prints declare -a MyString=([0]="a" [1]="p" [2]="a" [3]=$'\n' [4]="b" [5]="e" [6]="p" [7]="a")
As a response to Alexandro de Oliveira, I think the following is more elegant or at least more intuitive:
while read -r -n1 c ; do arr+=("$c") ; done <<<"hejsan"
declare -r some_string='abcdefghijklmnopqrstuvwxyz'
declare -a some_array
declare -i idx
for ((idx = 0; idx < ${#some_string}; ++idx)); do
some_array+=("${some_string:idx:1}")
done
for idx in "${!some_array[#]}"; do
echo "$((idx)): ${some_array[idx]}"
done
Pure bash, no loop.
Another solution, similar to/adapted from Léa Gris' solution, but using read -a instead of readarray/mapfile :
#!/usr/bin/env bash
str='azerty'
# Need extglob for the replacement pattern
shopt -s extglob
# Split string characters into array
# ${str//?()/$'\x1F'} replace each character "c" with "^_c".
# ^_ (Control-_, 0x1f) is Unit Separator (US), you can choose another
# character.
IFS=$'\x1F' read -ra array <<< "${str//?()/$'\x1F'}"
# now, array[0] contains an empty string and the rest of array (starting
# from index 1) contains the original string characters :
declare -p array
# Or, if you prefer to keep the array "clean", you can delete
# the first element and pack the array :
unset array[0]
array=("${array[#]}")
declare -p array
However, I prefer the shorter (and easier to understand for me), where we remove the initial 0x1f before assigning the array :
#!/usr/bin/env bash
str='azerty'
shopt -s extglob
tmp="${str//?()/$'\x1F'}" # same as code above
tmp=${tmp#$'\x1F'} # remove initial 0x1f
IFS=$'\x1F' read -ra array <<< "$tmp" # assign array
declare -p array # verification
In bash, given an arbitrary string containing ANSI CSI codes (eg colours), how do I emit a subset of the printable characters, printed in the correct colours?
Eg, given:
s=$'\e[0;1;31mRED\e[0;1;32mGREEN\e[0;1;33mYELLOW'
How do I do something like:
coloursubstr "$s" 0 5
coloursubstr "$s" 2 7
With bash and GNU grep:
coloursubstr() {
local string="$1" from="$2" num="$3"
local line i array=()
# fill array
while IFS= read -r line; do
[[ $line =~ ^([^m]+m)(.*)$ ]]
for ((i=0;i<${#BASH_REMATCH[2]};i++)); do
array+=("${BASH_REMATCH[1]}${BASH_REMATCH[2]:$i:1}")
done
done < <(grep -Po $'\x1b.*?m[^\x1b]*' <<< "$string")
# print array
for ((i=$from;i<$from+$num;i++)); do
printf "%s" "${array[$i]}"
done
echo
}
s=$'\e[0;1;31mRED\e[0;1;32mGREEN\e[0;1;33mYELLOW'
coloursubstr "$s" 0 5
coloursubstr "$s" 2 7
Output:
I assume all color codes start with \e, end with m and text is prefixed by a color code.
Partial answer, (specific hack with magic numbers, not at all general):
echo "${s:0:23}"
echo "${s:0:9}${s:11:25}"
Output:
Say you have a simple loop
while read line
do
printf "${line#*//}\n"
done < text.txt
Is there an elegant way of printing the current iteration with the output? Something like
0 The
1 quick
2 brown
3 fox
I am hoping to avoid setting a variable and incrementing it on each loop.
To do this, you would need to increment a counter on each iteration (like you are trying to avoid).
count=0
while read -r line; do
printf '%d %s\n' "$count" "${line*//}"
(( count++ ))
done < test.txt
EDIT: After some more thought, you can do it without a counter if you have bash version 4 or higher:
mapfile -t arr < test.txt
for i in "${!arr[#]}"; do
printf '%d %s' "$i" "${arr[i]}"
done
The mapfile builtin reads the entire contents of the file into the array. You can then iterate over the indices of the array, which will be the line numbers and access that element.
You don't often see it, but you can have multiple commands in the condition clause of a while loop. The following still requires an explicit counter variable, but the arrangement may be more suitable or appealing for some uses.
while ((i++)); read -r line
do
echo "$i $line"
done < inputfile
The while condition is satisfied by whatever the last command returns (read in this case).
Some people prefer to include the do on the same line. This is what that would look like:
while ((i++)); read -r line; do
echo "$i $line"
done < inputfile
You can use a range to go through, it can be an array, a string, a input line or a list.
In this example, i use a list of numbers [0..10] is used with an increment of 2, as well.
#!/bin/bash
for i in {0..10..2}; do
echo " $i times"
done
The output is:
0 times
2 times
4 times
6 times
8 times
10 times
To print the index regardless of the loop range, you have to use a variable "COUNTER=0" and increase it in each iteration "COUNTER+1".
my solution prints each iteration, the FOR traverses an inputline and increments by one each iteration, also shows each of words in the inputline:
#!/bin/bash
COUNTER=0
line="this is a sample input line"
for word in $line; do
echo "This i a word number $COUNTER: $word"
COUNTER=$((COUNTER+1))
done
The output is:
This i a word number 0: this
This i a word number 1: is
This i a word number 2: a
This i a word number 3: sample
This i a word number 4: input
This i a word number 5: line
to see more about loops: enter link description here
to test your scripts: enter link description here
n=0
cat test.txt | while read line; do
printf "%7s %s\n" "$n" "${line#*//}"
n=$((n+1))
done
This will work in Bourne shell as well, of course.
If you really want to avoid incrementing a variable, you can pipe the output through grep or awk:
cat test.txt | while read line; do
printf " %s\n" "${line#*//}"
done | grep -n .
or
awk '{sub(/.*\/\//, ""); print NR,$0}' test.txt
Update: Other answers posted here are better, especially those of #Graham and #DennisWilliamson.
Something very like this should suit:
tr -s ' ' '\n' <test.txt | nl -ba
You can add a -v0 flag to the nl command if you want indexing from 0.
I have a string containing many words with at least one space between each two. How can I split the string into individual words so I can loop through them?
The string is passed as an argument. E.g. ${2} == "cat cat file". How can I loop through it?
Also, how can I check if a string contains spaces?
I like the conversion to an array, to be able to access individual elements:
sentence="this is a story"
stringarray=($sentence)
now you can access individual elements directly (it starts with 0):
echo ${stringarray[0]}
or convert back to string in order to loop:
for i in "${stringarray[#]}"
do
:
# do whatever on $i
done
Of course looping through the string directly was answered before, but that answer had the the disadvantage to not keep track of the individual elements for later use:
for i in $sentence
do
:
# do whatever on $i
done
See also Bash Array Reference.
Did you try just passing the string variable to a for loop? Bash, for one, will split on whitespace automatically.
sentence="This is a sentence."
for word in $sentence
do
echo $word
done
This
is
a
sentence.
Probably the easiest and most secure way in BASH 3 and above is:
var="string to split"
read -ra arr <<<"$var"
(where arr is the array which takes the split parts of the string) or, if there might be newlines in the input and you want more than just the first line:
var="string to split"
read -ra arr -d '' <<<"$var"
(please note the space in -d ''; it cannot be omitted), but this might give you an unexpected newline from <<<"$var" (as this implicitly adds an LF at the end).
Example:
touch NOPE
var="* a *"
read -ra arr <<<"$var"
for a in "${arr[#]}"; do echo "[$a]"; done
Outputs the expected
[*]
[a]
[*]
as this solution (in contrast to all previous solutions here) is not prone to unexpected and often uncontrollable shell globbing.
Also this gives you the full power of IFS as you probably want:
Example:
IFS=: read -ra arr < <(grep "^$USER:" /etc/passwd)
for a in "${arr[#]}"; do echo "[$a]"; done
Outputs something like:
[tino]
[x]
[1000]
[1000]
[Valentin Hilbig]
[/home/tino]
[/bin/bash]
As you can see, spaces can be preserved this way, too:
IFS=: read -ra arr <<<' split : this '
for a in "${arr[#]}"; do echo "[$a]"; done
outputs
[ split ]
[ this ]
Please note that the handling of IFS in BASH is a subject on its own, so do your tests; some interesting topics on this:
unset IFS: Ignores runs of SPC, TAB, NL and on line starts and ends
IFS='': No field separation, just reads everything
IFS=' ': Runs of SPC (and SPC only)
Some last examples:
var=$'\n\nthis is\n\n\na test\n\n'
IFS=$'\n' read -ra arr -d '' <<<"$var"
i=0; for a in "${arr[#]}"; do let i++; echo "$i [$a]"; done
outputs
1 [this is]
2 [a test]
while
unset IFS
var=$'\n\nthis is\n\n\na test\n\n'
read -ra arr -d '' <<<"$var"
i=0; for a in "${arr[#]}"; do let i++; echo "$i [$a]"; done
outputs
1 [this]
2 [is]
3 [a]
4 [test]
BTW:
If you are not used to $'ANSI-ESCAPED-STRING' get used to it; it's a timesaver.
If you do not include -r (like in read -a arr <<<"$var") then read does backslash escapes. This is left as exercise for the reader.
For the second question:
To test for something in a string I usually stick to case, as this can check for multiple cases at once (note: case only executes the first match, if you need fallthrough use multiple case statements), and this need is quite often the case (pun intended):
case "$var" in
'') empty_var;; # variable is empty
*' '*) have_space "$var";; # have SPC
*[[:space:]]*) have_whitespace "$var";; # have whitespaces like TAB
*[^-+.,A-Za-z0-9]*) have_nonalnum "$var";; # non-alphanum-chars found
*[-+.,]*) have_punctuation "$var";; # some punctuation chars found
*) default_case "$var";; # if all above does not match
esac
So you can set the return value to check for SPC like this:
case "$var" in (*' '*) true;; (*) false;; esac
Why case? Because it usually is a bit more readable than regex sequences, and thanks to Shell metacharacters it handles 99% of all needs very well.
Just use the shells "set" built-in. For example,
set $text
After that, individual words in $text will be in $1, $2, $3, etc. For robustness, one usually does
set -- junk $text
shift
to handle the case where $text is empty or start with a dash. For example:
text="This is a test"
set -- junk $text
shift
for word; do
echo "[$word]"
done
This prints
[This]
[is]
[a]
[test]
$ echo "This is a sentence." | tr -s " " "\012"
This
is
a
sentence.
For checking for spaces, use grep:
$ echo "This is a sentence." | grep " " > /dev/null
$ echo $?
0
$ echo "Thisisasentence." | grep " " > /dev/null
$ echo $?
1
echo $WORDS | xargs -n1 echo
This outputs every word, you can process that list as you see fit afterwards.
(A) To split a sentence into its words (space separated) you can simply use the default IFS by using
array=( $string )
Example running the following snippet
#!/bin/bash
sentence="this is the \"sentence\" 'you' want to split"
words=( $sentence )
len="${#words[#]}"
echo "words counted: $len"
printf "%s\n" "${words[#]}" ## print array
will output
words counted: 8
this
is
the
"sentence"
'you'
want
to
split
As you can see you can use single or double quotes too without any problem
Notes:
-- this is basically the same of mob's answer, but in this way you store the array for any further needing. If you only need a single loop, you can use his answer, which is one line shorter :)
-- please refer to this question for alternate methods to split a string based on delimiter.
(B) To check for a character in a string you can also use a regular expression match.
Example to check for the presence of a space character you can use:
regex='\s{1,}'
if [[ "$sentence" =~ $regex ]]
then
echo "Space here!";
fi
For checking spaces just with bash:
[[ "$str" = "${str% *}" ]] && echo "no spaces" || echo "has spaces"
$ echo foo bar baz | sed 's/ /\n/g'
foo
bar
baz
For my use case, the best option was:
grep -oP '\w+' file
Basically this is a regular expression that matches contiguous non-whitespace characters. This means that any type and any amount of whitespace won't match. The -o parameter outputs each word matches on a different line.
Another take on this (using Perl):
$ echo foo bar baz | perl -nE 'say for split /\s/'
foo
bar
baz