Questions tagged [here-string]
A special, more compact form of the here-document consisting of <<< followed by a single WORD.
42 questions
4
votes
3
answers
721
views
How to remove 'newline' from 'here string'
The 'here string' (<<<) is a useful construct, and can be used in lieu of echo in many situations. However, when calculating a hash (as one example) the addition of a newline character ...
- 3,896
2
votes
1
answer
170
views
bash: what's the difference between '< file' and taking input from a here-string which contains the file?
I have a variable foo_var which contains ASCII text (base64 text, with some additional text which includes dashes, spaces, and underscores). I write this var to a file as follows:
cat <<<&...
- 391
5
votes
3
answers
2k
views
"Here Document" as a Single Line Command?
I have this command to run a checksum in some software I want to install:
echo "85762db0edc00ce19a2cd5496d1627903e6198ad850bbbdefb2ceaa46bd20cbd install.sh" | sha256sum -c
But I would like ...
- 51
-1
votes
2
answers
482
views
Difference in bash 3 between pipe and here-string
If I run:
IFS=':' cat <<< $(echo $PATH)
then the ":" are used for word splitting and the output contains spaces instead of ":", but if I run:
echo $PATH | IFS=':' cat
...
- 206
-2
votes
2
answers
719
views
How to use positional parameter in docker exec command with here strings (<<<)?
Here is what I am trying to do:
docker exec -it $1 /bin/bash <<< $CONTAINER_ID
But this doesn't work:
Output: "docker exec" requires at least 2 arguments.
It seems that <<...
7
votes
3
answers
2k
views
How can I use the bash <<< operator with diff?
Please, observe:
$ diff <(echo a) <<<b
diff: missing operand after '/dev/fd/63'
diff: Try 'diff --help' for more information.
I know <(...) works fine:
$ diff <(echo a) <(echo b)
...
- 379
1
vote
1
answer
245
views
How can I concat results in the here document?
I have this script:
while read $item;
do
# Some bash logic here
done <<< "$({ cat /path/to/some/file; echo; })"
Now I want to also use find to find the name of some directories,...
- 841
0
votes
1
answer
65
views
When would someone choose to use a limit string (<<-) instead of format here strings the normal way with <<<?
The - option to mark a here document limit string (<<-LimitString) will suppress leading tabs (but not spaces) in the output.
What I'm wondering is why someone would want to remove the leading ...
- 217
1
vote
2
answers
463
views
How to make a script fail when there is an error in here string?
I have a script similar to this:
#!/bin/bash
set -euo pipefail
IFS=$'\n\t'
while read -r l; do
echo "${l}"
done <<< "$(cat input.txt)"
echo Success
The command cat ...
- 155
2
votes
0
answers
139
views
Why does `rm writeprotectedfile <<< ""` delete the file?
The default behaviour of the GNU rm command when asked to delete write-protected files is to interactively ask whether the user wants to delete each of the files. This is quite inconvenient in many ...
- 662
2
votes
1
answer
279
views
sed with here-string fails, but succeeds when echo output piped to sed
After updating sed to 4.4 version, sed doesn't replace spaces with commas in the output of find command given to it as here-string:
sed --version
sed (GNU sed) 4.4
ls -l /tmp/test/
total 0
-rw-r--r-- ...
- 419
6
votes
2
answers
1k
views
What is more efficient or recommended for reading output of a command into variables in Bash?
If you want to read the single line output of a system command into Bash shell variables, you have at least two options, as in the examples below:
IFS=: read user x1 uid gid x2 home shell <<<...
- 618
3
votes
1
answer
501
views
backtick or Here string or read is not working as expected in RHEL 8
I am trying to redirect the output of a python script as an input into an interactive shell script.
test.py
print('Hello')
print('world')
Say test.py is as above prints "Hello world" which ...
- 143
1
vote
2
answers
608
views
sshpass Solaris one liner passing a command
I am trying to pass one liner sshpass command to Solaris box but won't work. those are the options I tried:
sshpass -p "passw" ssh "[email protected]" -o StrictHostKeyChecking=no `...
- 145
2
votes
2
answers
2k
views
Output tee to stdout while writing to a FD using here-strings
I am trying to output tee while writing to a custom file descriptor. Example:
exec 4>"/tmp/testfile.txt"; # open FD 4
tee -a >&4 <<< "Output this to stdout" # ...
- 123
4
votes
1
answer
5k
views
Why does a Bash 'while' read loop with a command substitution herestring not read the entire input?
Look at this very basic Bash script:
#!/bin/bash
while read l
do
echo $l
echo "next one"
done <<< $(ps aux)
I have several processes on my computer, and the ps aux command works fine in ...
- 173
0
votes
0
answers
286
views
SSH tty session as a Here String
At my job, the only way that I can switch users is by doing the following:
sudo su - *USER*
In order to run multiple commands as the user (in a script or something), I use here strings and here docs:
...
- 1
5
votes
1
answer
267
views
What is really happening in this command?
When I use the command cat <<< Hey > text.txt text.txt I expect it to write "Hey" in the file text.txt and then display the file. But there is no output. How is bash interpreting it ...
- 331
0
votes
2
answers
458
views
Ubuntu - How do I pass JSON string to herestring?
Update
I noticed that I am able to pass JSON with this command
command -j /dev/stdin <<< '{"key":"value"}'
However, it does not work if I call it through SSH.
ssh {target} 'command -j /dev/...
- 139
-1
votes
2
answers
1k
views
The need for $1 and $2 for comparison with an here-string
This is a follow up to this question;
I don't know why but I keep misunderstanding the following code, although I try very hard to understand it:
function read_and_verify {
read -p "$1:" tmp1
...
user149572
-1
votes
2
answers
673
views
What is the end of here string?
It seemed to me that the end of a here string is newline. I realize I am wrong:
$ cat <<< hello world
cat: world: No such file or directory
What can signify the end of a here string?
- 107k
11
votes
1
answer
2k
views
What are the differences between here document and here string in their purposes? [closed]
In bash, it seems to me both here document and here string can be used for providing strings as stdin inputs. here document may provide an extra features to specify delimiter, which I am not sure if ...
- 107k
6
votes
2
answers
1k
views
Are Here-Strings available in ksh88?
I wanted to extract 3 words from a variable in 3 different variables in ksh script. I used this line on ksh93 and it worked fine:
read A B C <<< $line
Got this error for the above command ...
- 649
19
votes
3
answers
30k
views
Cannot create temp file for here-document: Permission denied
[Note: This similar Q concerns the same bash error message. It's been marked a duplicate of this other Q. But because I found a very different source for this error, I will answer my own Q below.]
...
- 4,379
3
votes
3
answers
11k
views
Redirect content under a new line (without further syntax or arguments)
I tried these ways to append content to a file:
printf "\nsource ~/script.sh" >> /etc/bash.bashrc
echo -e "\nsource ~/script.sh" >> /etc/bash.bashrc
cat >> "/etc/bash.bashrc" <&...
- 4,523
12
votes
2
answers
4k
views
Why does wc <<<"$string" show a one-byte-longer length than printf "$string" | wc?
Accidentially, I found out that wc counts differently depending on how it gets the input from bash:
$ s='hello'
$ wc -m <<<"$s"
6
$ wc -c <<<"$s"
6
$ printf '%s' "$s" | wc -m
5
$ ...
- 1,359
2
votes
2
answers
1k
views
From multiline heredocument to a uniline herestring, with line breaks
I have this multilinie heredocument which I desire to translate into a uniline herestring:
cat <<-"PHPCONF" > /etc/php/*/zz_overrides.ini
[PHP]
post_max_size = 200M
upload_max_filesize ...
- 4,523
4
votes
2
answers
14k
views
How to use mapfile/readarray
I have some code similar to this:
while read -r col1 col2 col3 col4 col5 col6 col7 col8 TRASH; do
echo -e "${col1}\n${col2}\n${col3}\n${col4}\n${col5}\n${col6}\n"
done< <(ll | tail -n+...
- 41.6k
-2
votes
3
answers
1k
views
Append herestring data to a file, if it doesn't already exist in that file (all in one line)
What will be an "elegant" one-line way to append a single line of data into the end of a file, with herestring, if this exact data isn't already in that file?
This is my herestring append pattern:
...
- 4,523
2
votes
3
answers
4k
views
How can pipe producer tell pipe consumer it has reached 'End of File'?" (un-named-pipe, not named-pipe)
I have an application which requires a producer to send filenames to a consumer, and have producer indicate to the consumer when the last filename has been sent and the end of file has been reached.
...
- 756
4
votes
3
answers
8k
views
Variable not interpreted with 'EOF'
This is my script:
var="lalallalal"
tee file.tex <<'EOF'
text \\ text \\
$var
EOF
Need to use 'EOF' (with quotes) because I can not use double slash (//) otherwise.
However, if I use the ...
- 49
7
votes
2
answers
9k
views
Single line heredocument - Possible in Bash?
I desire to run a cat heredocument in a single row instead the natural syntax of 3 rows (opener, content, and delimiter). My need to do so is mostly aesthetic as the redirected content aimed aimed to ...
user149572
11
votes
1
answer
2k
views
What is the advantage of using bash -c over using a here string?
Is there any real benefit to using bash -c 'some command' over using bash <<< 'some command'
They seem to achieve the same effect.
- 419
3
votes
1
answer
3k
views
Diff between a string and a file
Basically I want to check the difference of the same file before and after a sed
Tried to run:
diff /opt/postTrades.sh <<< $(sed 's/1\ MIN/10\ MIN/g' /opt/postTrades.sh)
and
diff <<&...
- 322
5
votes
1
answer
17k
views
Elegant way of diff'ing two variables?
I have $a and $b. I want to run diff on those.
The best I have come up with is:
diff <(cat <<<"$a") <(cat <<<"$b")
But I have the district feeling that I am missing a clever ...
- 37.6k
1
vote
1
answer
1k
views
Assign a value to a variable inside a loop
I have this code :
HOSTS="host1 host2"
For hostname in ${HOSTS} ;
do ssh -tt ${USERNAME}@${hostname} << EOF
HOSTSN="test"
echo ${HOSTSN}
exit
EOF
Done
The variable HOSTSN is empty, can you ...
- 113
3
votes
2
answers
10k
views
unexpected EOF while looking for matching `)'
I'm simply trying to get the output from a sql statement and store in bash variable. I am getting " unexpected EOF while looking for matching `)' " error.
I don't see what i'm doing wrong. Why am I ...
1
vote
0
answers
296
views
ksh type with herestring
I wanted to use Here String in conjunction with custom type in KSH. Unfortunately I am not able to tell what I am doing wrong.
#!/bin/ksh
typeset -T Type_t=(
typeset string='aaa'
function fc {
...
- 145
10
votes
4
answers
5k
views
Why does cut fail with bash and not zsh?
I create a file with tab-delimited fields.
echo foo$'\t'bar$'\t'baz$'\n'foo$'\t'bar$'\t'baz > input
I have the following script named zsh.sh
#!/usr/bin/env zsh
while read line; do
<<<$...
- 20.6k
1
vote
2
answers
4k
views
Use variables in here-string
To feed input to an interactive script, I've been using a here-string:
script <<< $'1 2\n3 4\n5 6\nq'
This effectively enters
1 2
3 4
5 6
q
into the script. But how can I replace one of ...
- 315
2
votes
3
answers
1k
views
Extract lines from text with string as input
How can extract lines that match the regexp string ^li from the text (not a file) below using sed or something?
linux
loan
litmus
launch
I tried grep but I couldn't find a way to search within a ...
- 801
2
votes
1
answer
218
views
Openssl generate invalid websocket security code
I need to write websocket server on GAWK. And server must handle user's Sec-WebSocket-Key by following algorithm (from RFC):
Concat key with 258EAFA5-E914-47DA-95CA-C5AB0DC85B11
Take sha-1 in binary ...
- 45