Suppose I have the following command in bash:
one | two
one runs for a long time producing a stream of output and two performs a quick operation on each line of that stream, but two doesn't work at all unless the first value it reads tells it how many values to read per line. one does not output that value, but I know what it is in advance (let's say it's 15). I want to send a 15\n through the pipe before the output of one. I do not want to modify one or two.
My first thought was to do:
echo "$(echo 15; one)" | two
That gives me the correct output, but it doesn't stream through the pipe at all until the command one finishes. I want the output to start streaming right away through the pipe, since it takes a long time to execute (months).
I also tried:
echo 15; one | two
Which, of course, outputs 15, but doesn't send it through the pipe to two.
Is there a way in bash to pass '15\n' through the pipe and then start streaming the output of one through the same pipe?
You just need the shell grouping construct:
{ echo 15; one; } | two
The spaces around the braces and the trailing semicolon are required.
To test:
one() { sleep 5; echo done; }
two() { while read line; do date "+%T - $line"; done; }
{ printf "%s\n" 1 2 3; one; } | two
16:29:53 - 1
16:29:53 - 2
16:29:53 - 3
16:29:58 - done
Use command grouping:
{ echo 15; one; } | two
Done!
You could do this with sed:
Example 'one' script, emits one line per second to show it's line buffered and running.
#!/bin/bash
while [ 1 ]; do
echo "TICK $(date)"
sleep 1
done
Then pipe that through this sed command, note that for your specific example 'ArbitraryText' will be the number of fields. I used ArbitraryText so that it's obvious that this is the inserted text. On OSX, -l is unbuffered with GNU Sed I believe it's -u
$ ./one | sed -l '1i\
> ArbitraryText
> '
What this does is it instructs sed to insert one line before processing the rest of your file, everything else will pass through untouched.
The end result is processed line-by-line without chunk buffering (or, waiting for the input script to finish)
ArbitraryText
TICK Fri Jun 28 13:26:56 PDT 2013
...etc
You should be able to then pipe that into 'two' as you would normally.
Related
I'm a beginner in bash and here is my problem. I have a file just like this one:
Azzzezzzezzzezzz...
Bzzzezzzezzzezzz...
Czzzezzzezzzezzz...
I try in a script to edit this file.ABC letters are unique in all this file and there is only one per line.
I want to replace the first e of each line by a number who can be :
1 in line beginning with an A,
2 in line beginning with a B,
3 in line beginning with a C,
and I'd like to loop this in order to have this type of result
Azzz1zzz5zzz1zzz...
Bzzz2zzz4zzz5zzz...
Czzz3zzz6zzz3zzz...
All the numbers here are random int variables between 0 and 9. I really need to start by replacing 1,2,3 in first exec of my loop, then 5,4,6 then 1,5,3 and so on.
I tried this
sed "0,/e/s/e/$1/;0,/e/s/e/$2/;0,/e/s/e/$3/" /tmp/myfile
But the result was this (because I didn't specify the line)
Azzz1zzz2zzz3zzz...
Bzzzezzzezzzezzz...
Czzzezzzezzzezzz...
I noticed that doing sed -i "/A/ s/$/ezzz/" /tmp/myfile will add ezzz at the end of A line so I tried this
sed -i "/A/ 0,/e/s/e/$1/;/B/ 0,/e/s/e/$2/;/C/ 0,/e/s/e/$3/" /tmp/myfile
but it failed
sed: -e expression #1, char 5: unknown command: `0'
Here I'm lost.
I have in a variable (let's call it number_of_e_per_line) the number of e in either A, B or C line.
Thank you for the time you take for me.
Just apply s command on the line that matches A.
sed '
/^A/{ s/e/$1/; }
/^B/{ s/e/$2/; }
# or shorter
/^C/s/e/$3/
'
s command by default replaces the first occurrence. You can do for example s/s/$1/2 to replace the second occurrence, s/e/$1/g (like "Global") replaces all occurrences.
0,/e/ specifies a range of lines - it filters lines from the first up until a line that matches /e/.
sed is not part of Bash. It is a separate (crude) programming language and is a very standard command. See https://www.grymoire.com/Unix/Sed.html .
Continuing from the comment. sed is a poor choice here unless all your files can only have 3 lines. The reason is sed processes each line and has no way to keep a separate count for the occurrences of 'e'.
Instead, wrapping sed in a script and keeping track of the replacements allows you to handle any file no matter the number of lines. You just loop and handle the lines one at a time, e.g.
#!/bin/bash
[ -z "$1" ] && { ## valiate one argument for filename provided
printf "error: filename argument required.\nusage: %s filename\n" "./$1" >&2
exit 1
}
[ -s "$1" ] || { ## validate file exists and non-empty
printf "error: file not found or empty '%s'.\n" "$1"
exit 1
}
declare -i n=1 ## occurrence counter initialized 1
## loop reading each line
while read -r line || [ -n "$line" ]; do
[[ $line =~ ^.*e.*$ ]] || continue ## line has 'e' or get next
sed "s/e/1/$n" <<< "$line" ## substitute the 'n' occurence of 'e'
((n++)) ## increment counter
done < "$1"
Your data file having "..." at the end of each line suggests your files is larger than the snippet posted. If you have lines beginning 'A' - 'Z', you don't want to have to write 26 separate /match/s/find/replace/ substitutions. And if you have somewhere between 3 and 26 (or more), you don't want to have to rewrite a different sed expression for every new file you are faced with.
That's why I say sed is a poor choice. You really have no way to make the task a generic task with sed. The downside to using a script is it will become a poor choice as the number of records you need to process increase (over 100000 or so just due to efficiency)
Example Use/Output
With the script in replace-e-incremental.sh and your data in file, you would do:
$ bash replace-e-incremental.sh file
Azzz1zzzezzzezzz...
Bzzzezzz1zzzezzz...
Czzzezzzezzz1zzz...
To Modify file In-Place
Since you make multiple calls to sed here, you need to redirect the output of the file to a temporary file and then replace the original by overwriting it with the temp file, e.g.
$ bash replace-e-incremental.sh file > mytempfile && mv -f mytempfile file
$ cat file
Azzz1zzzezzzezzz...
Bzzzezzz1zzzezzz...
Czzzezzzezzz1zzz...
Can someone please explain how these process substitutions are working.
(echo "YES")> >(read str; echo "1:${str}:first";)> >(read sstr; echo "2:$sstr:two")> >(read ssstr; echo "3:$ssstr:three")
Output
1:2:3:YES:three:two:first
I've figured out, that the 'ssstr'-Substitution got FD 60, sstr FD 61 and str FD 62. (right to left)
But how is (echo "YES") connected to input of FD60, and output of FD60 with input FD61 and so on and finally FD62 prints out on Terminal ?
All against the direction of the two redirections.
How are they nested, and how connected ?
Makes me crazy.
Ty.
First off, don't actually write code like this :)
The process substitutions are the constructs >(...). The (...)> isn't a specific construct; it's just a subshell followed by an output redirection.
This example is a single command (echo "YES") followed by three output redirections
> >(read str; echo "1:${str}:first";)
> >(read sstr; echo "2:$sstr:two")
> >(read ssstr; echo "3:$ssstr:three")
The last one is the one that is actually applied to the original command; something like echo word >foo >bar >baz would create all three files, but the output of echo would only be written to baz.
Similarly, all three process substitutions start a new process, but the output YES is only written to the last one. So read ssstr gets its input from echo YES.
At this point, I think you are seeing what amounts to undefined behavior. The three process substitutions run in the reverse order they were created, as if the OS pushed each process on to a stack as the next one is created, then schedules them by popping them off the stack, but I don't think that order is guaranteed by anything.
In each case, though, the standard input of each process substitution is fixed to the standard output of the command, which is whichever other process substitution just ran. In other words, the command ends up being similar to
echo YES | {
read ssstr
echo "3:$ssstr:three" | {
read sstr
echo "2:$sstr:two" | {
read str
echo "1:$str:one"
}
}
}
I wish to swap or transpose pairs of lines according to their line-numbers (e.g., switching the positions of lines 10 and 15) in multiple text files using a UNIX tool such as sed or awk.
For example, I believe this sed command should swap lines 14 and 26 in a single file:
sed -n '14p' infile_name > outfile_name
sed -n '26p' infile_name >> outfile_name
How can this be extended to work on multiple files? Any one-liner solutions welcome.
If you want to edit a file, you can use ed, the standard editor. Your task is rather easy in ed:
printf '%s\n' 14m26 26-m14- w q | ed -s file
How does it work?
14m26 tells ed to take line #14 and move it after line #26
26-m14- tells ed to take the line before line #26 (which is your original line #26) and move it after line preceding line #14 (which is where your line #14 originally was)
w tells ed to write the file
q tells ed to quit.
If your numbers are in a variable, you can do:
linea=14
lineb=26
{
printf '%dm%d\n' "$linea" "$lineb"
printf '%d-m%d-\n' "$lineb" "$linea"
printf '%s\n' w q
} | ed -s file
or something similar. Make sure that linea<lineb.
If you want robust in-place updating of your input files, use gniourf_gniourf's excellent ed-based answer
If you have GNU sed and want to in-place updating with multiple files at once, use
#potong's excellent GNU sed-based answer (see below for a portable alternative, and the bottom for an explanation)
Note: ed truly updates the existing file, whereas sed's -i option creates a temporary file behind the scenes, which then replaces the original - while typically not an issue, this can have undesired side effects, most notably, replacing a symlink with a regular file (by contrast, file permissions are correctly preserved).
Below are POSIX-compliant shell functions that wrap both answers.
Stdin/stdout processing, based on #potong's excellent answer:
POSIX sed doesn't support -i for in-place updating.
It also doesn't support using \n inside a character class, so [^\n] must be replaced with a cumbersome workaround that positively defines all character except \n that can occur on a line - this is a achieved with a character class combining printable characters with all (ASCII) control characters other than \n included as literals (via a command substitution using printf).
Also note the need to split the sed script into two -e options, because POSIX sed requires that a branching command (b, in this case) be terminated with either an actual newline or continuation in a separate -e option.
# SYNOPSIS
# swapLines lineNum1 lineNum2
swapLines() {
[ "$1" -ge 1 ] || { printf "ARGUMENT ERROR: Line numbers must be decimal integers >= 1.\n" >&2; return 2; }
[ "$1" -le "$2" ] || { printf "ARGUMENT ERROR: The first line number ($1) must be <= the second ($2).\n" >&2; return 2; }
sed -e "$1"','"$2"'!b' -e ''"$1"'h;'"$1"'!H;'"$2"'!d;x;s/^\([[:print:]'"$(printf '\001\002\003\004\005\006\007\010\011\013\014\015\016\017\020\021\022\023\024\025\026\027\030\031\032\033\034\035\036\037\177')"']*\)\(.*\n\)\(.*\)/\3\2\1/'
}
Example:
$ printf 'line 1\nline 2\nline 3\n' | swapLines 1 3
line 3
line 2
line 1
In-place updating, based on gniourf_gniourf's excellent answer:
Small caveats:
While ed is a POSIX utility, it doesn't come preinstalled on all platforms, notably not on Debian and the Cygwin and MSYS Unix-emulation environments for Windows.
ed always reads the input file as a whole into memory.
# SYNOPSIS
# swapFileLines lineNum1 lineNum2 file
swapFileLines() {
[ "$1" -ge 1 ] || { printf "ARGUMENT ERROR: Line numbers must be decimal integers >= 1.\n" >&2; return 2; }
[ "$1" -le "$2" ] || { printf "ARGUMENT ERROR: The first line number ($1) must be <= the second ($2).\n" >&2; return 2; }
ed -s "$3" <<EOF
H
$1m$2
$2-m$1-
w
EOF
}
Example:
$ printf 'line 1\nline 2\nline 3\n' > file
$ swapFileLines 1 3 file
$ cat file
line 3
line 2
line 1
An explanation of #potong's GNU sed-based answer:
His command swaps lines 10 and 15:
sed -ri '10,15!b;10h;10!H;15!d;x;s/^([^\n]*)(.*\n)(.*)/\3\2\1/' f1 f2 fn
-r activates support for extended regular expressions; here, notably, it allows use of unescaped parentheses to form capture groups.
-i specifies that the files specified as operands (f1, f2, fn) be updated in place, without backup, since no optional suffix for a backup file is adjoined to the -i option.
10,15!b means that all lines that do not (!) fall into the range of lines 10 through 15 should branch (b) implicitly to the end of the script (given that no target-label name follows b), which means that the following commands are skipped for these lines. Effectively, they are simply printed as is.
10h copies (h) line number 10 (the start of the range) to the so-called hold space, which is an auxiliary buffer.
10!H appends (H) every line that is not line 10 - which in this case implies lines 11 through 15 - to the hold space.
15!d deletes (d) every line that is not line 15 (here, lines 10 through 14) and branches to the end of the script (skips remaining commands). By deleting these lines, they are not printed.
x, which is executed only for line 15 (the end of the range), replaces the so-called pattern space with the contents of the hold space, which at that point holds all lines in the range (10 through 15); the pattern space is the buffer on which sed commands operate, and whose contents are printed by default (unless -n was specified).
s/^([^\n]*)(.*\n)(.*)/\3\2\1/ then uses capture groups (parenthesized subexpressions of the regular expression that forms the first argument passed to function s) to partition the contents of the pattern space into the 1st line (^([^\n]*)), the middle lines ((.*\n)), and the last line ((.*)), and then, in the replacement string (the second argument passed to function s), uses backreferences to place the last line (\3) before the middle lines (\2), followed by the first line (\1), effectively swapping the first and last lines in the range. Finally, the modified pattern space is printed.
As you can see, only the range of lines spanning the two lines to swap is held in memory, whereas all other lines are passed through individually, which makes this approach memory-efficient.
This might work for you (GNU sed):
sed -ri '10,15!b;10h;10!H;15!d;x;s/^([^\n]*)(.*\n)(.*)/\3\2\1/' f1 f2 fn
This stores a range of lines in the hold space and then swaps the first and last lines following the completion of the range.
The i flag edits each file (f1,f2 ... fn) in place.
With GNU awk:
awk '
FNR==NR {if(FNR==14) x=$0;if(FNR==26) y=$0;next}
FNR==14 {$0=y} FNR==26 {$0=x} {print}
' file file > file_with_swap
The use of the following helper script allows using the power of find ... -exec ./script '{}' l1 l2 \; to locate the target files and to swap lines l1 & l2 in each file in place. (it requires that there are no identical duplicate lines within the file that fall within the search range) The script uses sed to read the two swap lines from each file into an indexed array and passes the lines to sed to complete the swap by matching. The sed call uses its "matched first address" state to limit the second expression swap to the first occurrence. An example use of the helper script below to swap lines 5 & 15 in all matching files is:
find . -maxdepth 1 -type f -name "lnum*" -exec ../swaplines.sh '{}' 5 15 \;
For example, the find call above found files lnumorig.txt and lnumfile.txt in the present directory originally containing:
$ head -n20 lnumfile.txt.bak
1 A simple line of test in a text file.
2 A simple line of test in a text file.
3 A simple line of test in a text file.
4 A simple line of test in a text file.
5 A simple line of test in a text file.
6 A simple line of test in a text file.
<snip>
14 A simple line of test in a text file.
15 A simple line of test in a text file.
16 A simple line of test in a text file.
17 A simple line of test in a text file.
18 A simple line of test in a text file.
19 A simple line of test in a text file.
20 A simple line of test in a text file.
And swapped the lines 5 & 15 as intended:
$ head -n20 lnumfile.txt
1 A simple line of test in a text file.
2 A simple line of test in a text file.
3 A simple line of test in a text file.
4 A simple line of test in a text file.
15 A simple line of test in a text file.
6 A simple line of test in a text file.
<snip>
14 A simple line of test in a text file.
5 A simple line of test in a text file.
16 A simple line of test in a text file.
17 A simple line of test in a text file.
18 A simple line of test in a text file.
19 A simple line of test in a text file.
20 A simple line of test in a text file.
The helper script itself is:
#!/bin/bash
[ -z $1 ] && { # validate requierd input (defaults set below)
printf "error: insufficient input calling '%s'. usage: file [line1 line2]\n" "${0//*\//}" 1>&2
exit 1
}
l1=${2:-10} # default/initialize line numbers to swap
l2=${3:-15}
while IFS=$'\n' read -r line; do # read lines to swap into indexed array
a+=( "$line" );
done <<<"$(sed -n $((l1))p "$1" && sed -n $((l2))p "$1")"
((${#a[#]} < 2)) && { # validate 2 lines read
printf "error: requested lines '%d & %d' not found in file '%s'\n" $l1 $l2 "$1"
exit 1
}
# swap lines in place with sed (remove .bak for no backups)
sed -i.bak -e "s/${a[1]}/${a[0]}/" -e "0,/${a[0]}/s/${a[0]}/${a[1]}/" "$1"
exit 0
Even though I didn't manage to get it all done in a one-liner I decided it was worth posting in case you can make some use of it or take ideas from it. Note: if you do make use of it, test to your satisfaction before turning it loose on your system. The script currently uses sed -i.bak ... to create backups of the files changed for testing purposes. You can remove the .bak when you are satisfied it meets your needs.
If you have no use for setting default lines to swap in the helper script itself, then I would change the first validation check to [ -z $1 -o -z $2 -o $3 ] to insure all required arguments are given when the script is called.
While it does identify the lines to be swapped by number, it relies on the direct match of each line to accomplish the swap. This means that any identical duplicate lines up to the end of the swap range will cause an unintended match and failue to swap the intended lines. This is part of the limitation imposed by not storing each line within the range of lines to be swapped as discussed in the comments. It's a tradeoff. There are many, many ways to approach this, all will have their benefits and drawbacks. Let me know if you have any questions.
Brute Force Method
Per your comment, I revised the helper script to use the brute forth copy/swap method that would eliminate the problem of any duplicate lines in the search range. This helper obtains the lines via sed as in the original, but then reads all lines from file to tmpfile swapping the appropriately numbered lines when encountered. After the tmpfile is filled, it is copied to the original file and tmpfile is removed.
#!/bin/bash
[ -z $1 ] && { # validate requierd input (defaults set below)
printf "error: insufficient input calling '%s'. usage: file [line1 line2]\n" "${0//*\//}" 1>&2
exit 1
}
l1=${2:-10} # default/initialize line numbers to swap
l2=${3:-15}
while IFS=$'\n' read -r line; do # read lines to swap into indexed array
a+=( "$line" );
done <<<"$(sed -n $((l1))p "$1" && sed -n $((l2))p "$1")"
((${#a[#]} < 2)) && { # validate 2 lines read
printf "error: requested lines '%d & %d' not found in file '%s'\n" $l1 $l2 "$1"
exit 1
}
# create tmpfile, set trap, truncate
fn="$1"
rmtemp () { cp "$tmpfn" "$fn"; rm -f "$tmpfn"; }
trap rmtemp SIGTERM SIGINT EXIT
declare -i n=1
tmpfn="$(mktemp swap_XXX)"
:> "$tmpfn"
# swap lines in place with a tmpfile
while IFS=$'\n' read -r line; do
if ((n == l1)); then
printf "%s\n" "${a[1]}" >> "$tmpfn"
elif ((n == l2)); then
printf "%s\n" "${a[0]}" >> "$tmpfn"
else
printf "%s\n" "$line" >> "$tmpfn"
fi
((n++))
done < "$fn"
exit 0
If the line numbers to be swapped are fixed then you might want to try something like the sed command in the following example to have lines swapped in multiple files in-place:
#!/bin/bash
# prep test files
for f in a b c ; do
( for i in {1..30} ; do echo $f$i ; done ) > /tmp/$f
done
sed -i -s -e '14 {h;d}' -e '15 {N;N;N;N;N;N;N;N;N;N;G;x;d}' -e '26 G' /tmp/{a,b,c}
# -i: inplace editing
# -s: treat each input file separately
# 14 {h;d} # first swap line: hold ; suppress
# 15 {N;N;...;G;x;d} # lines between: collect, append held line; hold result; suppress
# 26 G # second swap line: append held lines (and output them all)
# dump test files
cat /tmp/{a,b,c}
(This is according to Etan Reisner's comment.)
If you want to swap two lines, you can send it through twice, you could make it loop in one sed script if you really wanted, but this works:
e.g.
test.txt: for a in {1..10}; do echo "this is line $a"; done >> test.txt
this is line 1
this is line 2
this is line 3
this is line 4
this is line 5
this is line 6
this is line 7
this is line 8
this is line 9
this is line 10
Then to swap lines 6 and 9:
sed ':a;6,8{6h;6!H;d;ba};9{p;x};' test.txt | sed '7{h;d};9{p;x}'
this is line 1
this is line 2
this is line 3
this is line 4
this is line 5
this is line 9
this is line 7
this is line 8
this is line 6
this is line 10
In the first sed it builds up the hold space with lines 6 through 8.
At line 9 it prints line 9 then prints the hold space (lines 6 through 8) this accomplishes the first move of 9 to place 6. Note: 6h; 6!H avoids a new line at the top of the pattern space.
The second move occurs in the second sed script it saves line 7 to the hold space, then deletes it and prints it after line 9.
To make it quasi-generic you can use variables like this:
A=3 && B=7 && sed ':a;'${A}','$((${B}-1))'{'${A}'h;'${A}'!H;d;ba};'${B}'{p;x};' test.txt | sed $(($A+1))'{h;d};'${B}'{p;x}'
Where A and B are the lines you want to swap, in this case lines 3 and 7.
if, you want swap two lines, to create script "swap.sh"
#!/bin/sh
sed -n "1,$((${2}-1))p" "$1"
sed -n "${3}p" "$1"
sed -n "$((${2}+1)),$((${3}-1))p" "$1"
sed -n "${2}p" "$1"
sed -n "$((${3}+1)),\$p" "$1"
next
sh swap.sh infile_name 14 26 > outfile_name
How to I concatenate stdin to a string, like this?
echo "input" | COMMAND "string"
and get
inputstring
A bit hacky, but this might be the shortest way to do what you asked in the question (use a pipe to accept stdout from echo "input" as stdin to another process / command:
echo "input" | awk '{print $1"string"}'
Output:
inputstring
What task are you exactly trying to accomplish? More context can get you more direction on a better solution.
Update - responding to comment:
#NoamRoss
The more idiomatic way of doing what you want is then:
echo 'http://dx.doi.org/'"$(pbpaste)"
The $(...) syntax is called command substitution. In short, it executes the commands enclosed in a new subshell, and substitutes the its stdout output to where the $(...) was invoked in the parent shell. So you would get, in effect:
echo 'http://dx.doi.org/'"rsif.2012.0125"
use cat - to read from stdin, and put it in $() to throw away the trailing newline
echo input | COMMAND "$(cat -)string"
However why don't you drop the pipe and grab the output of the left side in a command substitution:
COMMAND "$(echo input)string"
I'm often using pipes, so this tends to be an easy way to prefix and suffix stdin:
echo -n "my standard in" | cat <(echo -n "prefix... ") - <(echo " ...suffix")
prefix... my standard in ...suffix
There are some ways of accomplish this, i personally think the best is:
echo input | while read line; do echo $line string; done
Another can be by substituting "$" (end of line character) with "string" in a sed command:
echo input | sed "s/$/ string/g"
Why i prefer the former? Because it concatenates a string to stdin instantly, for example with the following command:
(echo input_one ;sleep 5; echo input_two ) | while read line; do echo $line string; done
you get immediatly the first output:
input_one string
and then after 5 seconds you get the other echo:
input_two string
On the other hand using "sed" first it performs all the content of the parenthesis and then it gives it to "sed", so the command
(echo input_one ;sleep 5; echo input_two ) | sed "s/$/ string/g"
will output both the lines
input_one string
input_two string
after 5 seconds.
This can be very useful in cases you are performing calls to functions which takes a long time to complete and want to be continuously updated about the output of the function.
You can do it with sed:
seq 5 | sed '$a\6'
seq 5 | sed '$ s/.*/\0 6/'
In your example:
echo input | sed 's/.*/\0string/'
I know this is a few years late, but you can accomplish this with the xargs -J option:
echo "input" | xargs -J "%" echo "%" "string"
And since it is xargs, you can do this on multiple lines of a file at once. If the file 'names' has three lines, like:
Adam
Bob
Charlie
You could do:
cat names | xargs -n 1 -J "%" echo "I like" "%" "because he is nice"
Also works:
seq -w 0 100 | xargs -I {} echo "string "{}
Will generate strings like:
string 000
string 001
string 002
string 003
string 004
...
The command you posted would take the string "input" use it as COMMAND's stdin stream, which would not produce the results you are looking for unless COMMAND first printed out the contents of its stdin and then printed out its command line arguments.
It seems like what you want to do is more close to command substitution.
http://www.gnu.org/software/bash/manual/html_node/Command-Substitution.html#Command-Substitution
With command substitution you can have a commandline like this:
echo input `COMMAND "string"`
This will first evaluate COMMAND with "string" as input, and then expand the results of that commands execution onto a line, replacing what's between the ‘`’ characters.
cat will be my choice: ls | cat - <(echo new line)
With perl
echo "input" | perl -ne 'print "prefix $_"'
Output:
prefix input
A solution using sd (basically a modern sed; much easier to use IMO):
# replace '$' (end of string marker) with 'Ipsum'
# the `e` flag disables multi-line matching (treats all lines as one)
$ echo "Lorem" | sd --flags e '$' 'Ipsum'
Lorem
Ipsum#no new line here
You might observe that Ipsum appears on a new line, and the output is missing a \n. The reason is echo's output ends in a \n, and you didn't tell sd to add a new \n. sd is technically correct because it's doing exactly what you are asking it to do and nothing else.
However this may not be what you want, so instead you can do this:
# replace '\n$' (new line, immediately followed by end of string) by 'Ipsum\n'
# don't forget to re-add the `\n` that you removed (if you want it)
$ echo "Lorem" | sd --flags e '\n$' 'Ipsum\n'
LoremIpsum
If you have a multi-line string, but you want to append to the end of each individual line:
$ ls
foo bar baz
$ ls | sd '\n' '/file\n'
bar/file
baz/file
foo/file
I want to prepend my sql script with "set" statement before running it.
So I echo the "set" instruction, then pipe it to cat. Command cat takes two parameters : STDIN marked as "-" and my sql file, cat joins both of them to one output. Next I pass the result to mysql command to run it as a script.
echo "set #ZERO_PRODUCTS_DISPLAY='$ZERO_PRODUCTS_DISPLAY';" | cat - sql/test_parameter.sql | mysql
p.s. mysql login and password stored in .my.cnf file
Normally I use something like this for processes I run on my servers
./runEvilProcess.sh >> ./evilProcess.log
However I'm currently using Doxygen and it produces lots of duplicate output
Example output:
QGDict::hashAsciiKey: Invalid null key
QGDict::hashAsciiKey: Invalid null key
QGDict::hashAsciiKey: Invalid null key
So you end up with a very messy log
Is there a way I can only add the line to the log file if the line wasn't the last one added.
A poor example (but not sure how to do in bash)
$previousLine = ""
$outputLine = getNextLine()
if($previousLine != $outputLine) {
$outputLine >> logfile.log
$previousLine = $outputLine
}
If the process returns duplicate lines in a row, pipe the output of your process through uniq:
$ ./t.sh
one
one
two
two
two
one
one
$ ./t.sh | uniq
one
two
one
If the logs are sent to the standard error stream, you'll need to redirect that too:
$ ./yourprog 2>&1 | uniq >> logfile
(This won't help if the duplicates come from multiple runs of the program - but then you can pipe your log file through uniq when reviewing it.)
Create a filter script (filter.sh):
while read line; do
if [ "$last" != "$line" ]; then
echo $line
last=$line
fi
done
and use it:
./runEvilProcess.sh | sh filter.sh >> evillog