" %}
```bash
python3 - << 'EOF'
print("Hello here doc!")
EOF
```
* Prints `Hello here doc!`
```bash
python3 - << 'EOF' | cat
import sys
sys.stdout.write("12345678")
EOF
```
* The *here-document* will feed text into *stdin* **of** `python3`
* The pipe **(`|`**) performs the following: *stdout* of `python3` -> stdin of `cat`
* Prints `12345678`
```bash
python3 - << 'EOF' >> outfile
import sys
sys.stdout.write("12345678")
EOF
```
* The *here-document* will feed text into *stdin* **of** `python3`
* The redirection (`>>`) will append the *stdout* of `python3` to the file `outfile`
* Appends `12345678` to the file
```bash
$ cat outfile
12345678
```
### 1.13 Example with while loop + read
```bash
Arr=(0 1 2 {A..D}) # (0 1 2 A B C D)
while read element ; do
echo "$element"
done <<< $(echo ${Arr[*]})
# output: 0 1 2 A B C D
```
* Print each value in the array from s*tdout*
* `echo` prints to the *stdout* (**fd 1**)
Arr=(0 1 2 {A..D}) # (0 1 2 A B C D)
while read element ; do
echo "$element" 1>&2 # >&2 works too since `>` defaults to stdout (fd 1)
done <<< $(echo ${Arr[*]})
# output: 0 1 2 A B C D
* Print each value in the array from *stderr*
* `1>&2` redirects *stdout* to *stderr*
Arr=(0 1 2 {A..D}) # (0 1 2 A B C D)
while read element ; do
echo "$element"
done <<< $(echo ${Arr[*]}) >> outfile
# output: empty
* `>> outfile` append *stdout* to the `outfile` file
* The file `outfile` will contain the value: **0 1 2 A B C D**
Arr=(0 1 2 {A..D}) # (0 1 2 A B C D)
while read element ; do
echo "$element" 1>&2 # >&2 works too since `>` defaults to stdout (fd 1)
done <<< $(echo ${Arr[*]}) >> outfile
# output: 0 1 2 A B C D
* Notice that even with the `>> outfile` command the data is not actually written to the file, but instead printed on the terminal
* This is due to the `1>&2` command redirecting *stdout* to *stderr*
* The value in stderr will be printed on the terminal
* The file `outfile` will be empty
```bash
# without 1>&2
while read element ; do
echo "$element"
done <<< $(echo ${Arr[*]}) &>/dev/null
# output: empty
while read element ; do
echo "$element" 1>&2
done <<< $(echo ${Arr[*]}) &>/dev/null
# output: empty
```
* Notice that the output is empty
* This is due to the `&>/dev/null` command at the end which redirect all the *stout* and *stderr* to the `/dev/null` file
{% embed url="" %}
## 2. Here Strings
{% embed url="" %}
### 2.1 Basic syntax
The here string (`<<<`) command is used for input redirection from a text or variable
```bash
[COMMAND] <<< 'string' # from text
[COMMAND] <<< $DATA # from variable
```
#### 2.12 Input redirection from a text
* Both commands shown below are equivalent
* outputs `hr`
```bash
echo "here" | tr -d 'e'
tr -d 'e' <<< "here"
```
#### 2.13 Input redirecton from a variable
```bash
DATA="here"
echo $DATA | tr -d 'e'
tr -d 'e' <<< $DATA
```
[^1]: redirect stdout to stderr
[^2]: append to `outfile`
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