import pathlib, subprocess
while True:
    app = pathlib.Path(input("$ "))
    try:
        subprocess.run(app)
    except Exception as ex:
        print(ex)

<input.txt ./app1.py >output1.txt; <output1.txt ./app2.py >output2.txt


%%sh

# myapp.sh
export MYAPP_HOME='/Users/slott/Documents/Writing/Python/Bashing the Bash/myapp-v1.2.3'
source "${MYAPP_HOME}/env_prod.sh"
python "${MYAPP_HOME}/myapp" $*

MyApp Settings
MYAPP_LOG='/myapp/db/log'
MYAPP_ENV='/myapp/db/prod'
MYAPP_HOME='/Users/slott/Documents/Writing/Python/Bashing the Bash/myapp-v1.2.3'

app1.py <input.txt | app2.py >output2.txt

echo What about ${MY_FAVORITE_FEATURE}?

import os; print(f"What about {os.environ['MY_FAVORITE_FEATURE']}?")

"""What about my favorite feature notification

>>> os.environ['MY_FAVORITE_FEATURE'] = "echo"
>>> main()
What about echo?
"""
import os
def main() -> None:
    print(f"What about {os.environ['MY_FAVORITE_FEATURE']}?")
if __name__ == "__main__":
    main()

pathlib.Path("b").write_bytes(pathlib.Path("a").read_bytes())

app1.py <input.txt >output.txt && cp output.txt ${BACKUP}/output.txt


import pathlib
import subprocess
import os

def app1() -> int:
    with pathlib.Path("input.txt").open() as input:
        with pathlib.Path("output.txt").open("w") as output:
            p = subprocess.run(["python", "app1.py"], stdin=input, stdout=output, check=False)
    return p.returncode

def cp() -> int:
    source = pathlib.Path("output.txt")
    target = pathlib.Path(os.environ.get("BACKUP", "/tmp")) / source.name
    target.write_bytes(source.read_bytes())
    return 0
        
def main() -> None:
    r1 = app1()
    if r1 == 0:  # The && operator
        r2 = cp()
        # exit(r2)  # Spooks Jupyter Lab

if __name__ == "__main__":
    main()

for f in *.txt
do
    nm=${f##.*}
    b=${n%.*}
    e=${n##*.}
    app2.py ${f} >${b}_a2.${e} || echo "Problem with ${f}"
done


import pathlib
import subprocess
import os

def app2(file: pathlib.Path) -> int:
    output_path = pathlib.Path.cwd() / f"{file.stem}_a2{file.suffix}"
    with file.open() as input:
        with output_path.open('w') as output:
            p = subprocess.run(["python", "app2.py"], stdin=input, stdout=output, check=False)
    return p.returncode

def echo(file: pathlib.Path) -> int:
    print(f"Problem with {file!s}")
    return 0

def main() -> None:
    for f in pathlib.Path.cwd().glob("*.txt"):
        r1 = app2(f)
        if r1 != 0:  # The || operator
            r2 = echo()
    # exit(0)

if __name__ == "__main__":
    main()


%%sh 

dc -e '5k 355 113 / p'

3.14159

dt=`date +"%Y-%m-%d"`
log=${dt}.log


import datetime
import pathlib

def log_path() -> pathlib.Path:
    now = datetime.datetime.now(datetime.timezone.utc)
    path = (
        pathlib.Path.cwd() / now.strftime("%Y-%m-%d")
    ).with_suffix(".log")
    return path

log_path()

PosixPath('/Users/slott/Documents/Writing/Python/Bashing the Bash/2022-06-12.log')

find . -name '*.txt' -exec app2.py <{} >{}.out \;


import pathlib
import subprocess

class App2:
    def run(self, input: pathlib.Path, output: pathlib.Path) -> None:
        with input.open() as source:
            with output.open('w') as target:
                subprocess.run(["python", "app2.py"], stdin=source, stdout=target, check=True)

def find_and_exec():
    app2 = App2()
    for path in pathlib.Path.cwd().glob("**/*_a2.txt"):
        app2.run(path, pathlib.Path(f"{path.name}.out"))
    
def main():
    find_and_exec()

if __name__ == "__main__":
    main()

find . \( -name '*_a2.txt' -or -name '*.txt.out' \) -print -delete >cleanup.log


import pathlib
import itertools
import contextlib

def main():
    matches = itertools.chain(
        pathlib.Path.cwd().glob("**/*_a2.txt"),
        pathlib.Path.cwd().glob("**/*.txt.out")
    )
    for path in matches:
        print(path)
        path.unlink()

if __name__ == "__main__":
    log = pathlib.Path("cleanup.log")
    with log.open("w") as log_file:
        with contextlib.redirect_stdout(log_file):
            main()

for d in ${DIRECTORIES}
do
    fixups=`grep --with-filename 'print\s*(' ${d}/*.py | awk -F: '{print $1}' | sort -u`
    for f in fixups
    do
        echo fixing ${f}
        cat $f | sed 's/print/logger.info/' | awk 'BEGIN {print "import logging\nlogger = logging.getLogger(__file__)\n"} {print $0}' > ${f}.new
    done
done

repos=`curl https://api.github.com/users/slott56 | jq '.repos_url'`
curl $repos

Bashing the Bash¶

Why the Shell is Awful¶

Writing Safe Shell Scripts¶

Agenda¶

Link¶

1. Why we need the shell¶

Single-app Linux server¶

Secure single-app server¶

Interactive users, however...¶

Let Me Repeat That¶

The shell is complicated¶

Secondary use case¶

Programming In The Large¶

There's no bright line¶

Script file vs. C code¶

A few more complications¶

Safe Shell Scripts are Small¶

2. Why The Shell Is Awful¶

What the shell does well¶

Process algebra¶

No unit testing¶

3. What Can We Do?¶

Did you mean this?¶

What About Unit Tests?¶

It's so long... 😭¶

Use cases for the shell¶

Filesystem operations¶

Conditional Processing¶

It's too much code¶

Iterative processsing¶

Math¶

Date/Time¶

Making filenames¶

The find command¶

Using pathlib¶

grep | sed | awk¶

Stop. Breathe. Think.¶

Parsing¶

Concurrent pipelines¶

4. Conclusion¶

The Myth of One-Time Scripts¶

Myth, continued...¶

Common script-writing contexts¶

I need to write an installer¶

Design Patterns¶

The Shell is Awful¶

Hard (almost impossible) to test¶

Too easy to tweak and break¶

Very hard to read and understand¶

Hard to handle edge cases and exceptions¶

The `find` command¶

Using `pathlib`¶